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# Data Science Interview Questions and Answers

Data Science Interview Questions and Answers for beginners and experts. List of frequently asked Data Science Interview Questions with answers by Besant Technologies.

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### Best Data Science Interview Questions and Answers

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### Data Science Interview Questions and Answers for Placements

Here is the list of most frequently asked Data Science Interview Questions and Answers in technical interviews. These Data Science questions and answers are suitable for both freshers and experienced professionals at any level. The questions are for intermediate to somewhat advanced Data Science professionals, but even if you are just a beginner or fresher you should be able to understand the answers and explanations here we give.

In this post, you will get the most important and top 150+ Data science Interview Questions and Answers, which will be very helpful and useful to those who are preparing for jobs.

Start by fitting a simple model (multivariate regression, logistic regression), do some feature engineering accordingly, and then try some complicated models. Always split the dataset into train, validation, test dataset and use cross validation to check their performance.

Determine if the problem is classification or regression

Favor simple models that run quickly and you can easily explain.

Mention cross validation as a means to evaluate the model.

Plot and visualize the data.

The model that has high training accuracy might have low test accuracy. Without further knowledge, it is hard to know which dataset represents the population data and thus the generalizability of the algorithm is hard to measure. This should be mitigated by repeated splitting of train vs test dataset (as in cross validation).

When there is a change in data distribution, this is called the dataset shift. If the train and test data has a different distribution, then the classifier would likely overfit to the train data.

This issue can be overcome by using a more general learning method.

This can occur when:

P(y|x) are the same but P(x) are different. (covariate shift)

P(y|x) are different. (concept shift)

The causes can be:

Training samples are obtained in a biased way. (sample selection bias)

Train is different from test because of temporal, spatial changes. (non-stationary environments)

Solution to covariate shift

importance weighted cv

We can have regularization such as L1 or L2 to reduce variance (increase bias).

Changes to the algorithm:

Use tree-based methods instead of regression methods as they are more resistant to outliers. For statistical tests, use non parametric tests instead of parametric ones.

Use robust error metrics such as MAE or Huber Loss instead of MSE.

Changes to the data:

Winsorizing the data

Transforming the data (e.g. log)

Remove them only if you’re certain they’re anomalies not worth predicting

MSE is more strict to having outliers. MAE is more robust in that sense, but is harder to fit the model for because it cannot be numerically optimized. So when there are less variability in the model and the model is computationally easy to fit, we should use MAE, and if that’s not the case, we should use MSE.

MSE: easier to compute the gradient, MAE: linear programming needed to compute the gradient

MAE more robust to outliers. If the consequences of large errors are great, use MSE

MSE corresponds to maximizing likelihood of Gaussian random variables

Accuracy: proportion of instances you predict correctly. Pros: intuitive, easy to explain, Cons: works poorly when the class labels are imbalanced and the signal from the data is weak

AUROC: plot fpr on the x axis and tpr on the y axis for different threshold. Given a random positive instance and a random negative instance, the AUC is the probability that you can identify who’s who. Pros: Works well when testing the ability of distinguishing the two classes, Cons: can’t interpret predictions as probabilities (because AUC is determined by rankings), so can’t explain the uncertainty of the model

logloss/deviance: Pros: error metric based on probabilities, Cons: very sensitive to false positives, negatives

When there are more than 2 groups, we can have k binary classifications and add them up for logloss. Some metrics like AUC is only applicable in the binary case.

Things to look at: N, P, linearly seperable?, features independent?, likely to overfit?, speed, performance, memory usage

Logistic Regression:

features roughly linear, problem roughly linearly separable

robust to noise, use l1,l2 regularization for model selection, avoid overfitting

the output come as probabilities

efficient and the computation can be distributed

can be used as a baseline for other algorithms

(-) can hardly handle categorical features

SVM:

with a nonlinear kernel, can deal with problems that are not linearly separable

(-) slow to train, for most industry scale applications, not really efficient

Naive Bayes:

computationally efficient when P is large by alleviating the curse of dimensionality

works surprisingly well for some cases even if the condition doesn’t hold

with word frequencies as features, the independence assumption can be seen reasonable. So the algorithm can be used in text categorization

(-) conditional independence of every other feature should be met

Tree Ensembles:

good for large N and large P, can deal with categorical features very well

non parametric, so no need to worry about outliers

GBT’s work better but the parameters are harder to tune

RF works out of the box, but usually performs worse than GBT

Deep Learning:

works well for some classification tasks (e.g. image)

used to squeeze something out of the problem

Regularization is useful for reducing variance in the model, meaning avoiding overfitting . For example, we can use L1 regularization in Lasso regression to penalize large coefficients.

When we add irrelevant features, it increases model’s tendency to overfit because those features introduce more noise. When two variables are correlated, they might be harder to interpret in case of regression, etc.

curse of dimensionality

adding random noise makes the model more complicated but useless

computational cost

Ask someone for more details.

Build a time series model with the training data with a seven day cycle and then use that for a new data with only 2 days data.

Ask someone for more details.

Build a regression function to estimate the number of retweets as a function of time t

to determine if one regression function can be built, see if there are clusters in terms of the trends in the number of retweets

if not, we have to add features to the regression function

features + # of retweets on the first and the second day -> predict the seventh day

https://en.wikipedia.org/wiki/Dynamic_time_warping

We can collect social media data using twitter, Facebook, instagram API’s. Then, for example, for twitter, we can construct features from each tweet, e.g. the tweeted date, number of favorites, retweets, and of course, the features created from the tweeted content itself. Then use a multi variate time series model to predict the weather.

Ask someone for more details. Get Data Science Training in Kalayan Nagar Bangalore.

We can do so using building a recommendation engine. The easiest we can do is to show contents that are popular other users, which is still a valid strategy if for example the contents are news articles. To be more accurate, we can build a content based filtering or collaborative filtering. If there’s enough user usage data, we can try collaborative filtering and recommend contents other similar users have consumed. If there isn’t, we can recommend similar items based on vectorization of items (content based filtering).

Find strong unconnected people in weighted connection graph

Define similarity as how strong the two people are connected

Given a certain feature, we can calculate the similarity based on

friend connections (neighbors)

Check-in’s people being at the same location all the time.

same college, workplace

Have randomly dropped graphs test the performance of the algorithm

ref. News Feed Optimization

Affinity score: how close the content creator and the users are

Weight: weight for the edge type (comment, like, tag, etc.). Emphasis on features the company wants to promote

Time decay: the older the less important

for each user, assign a score of how likely someone would send an email to

the rest is feature engineering:

number of past emails, how many responses, the last time they exchanged an email, whether the last email ends with a question mark, features about the other users, etc.

Ask someone for more details.

People who someone sent emails the most in the past, conditioning on time decay.

build a master dataset with local demographic information available for each location.

local income levels, proximity to traffic, weather, population density, proximity to other businesses

a reference dataset on local, regional, and national macroeconomic conditions (e.g. unemployment, inflation, prime interest rate, etc.)

any data on the local franchise owner-operators, to the degree the manager

identify a set of KPIs acceptable to the management that had requested the analysis concerning the most desirable factors surrounding a franchise

quarterly operating profit, ROI, EVA, pay-down rate, etc.

run econometric models to understand the relative significance of each variable

run machine learning algorithms to predict the performance of each location candidate

Based on the past frequencies of words shown up given a sequence of words, we can construct conditional probabilities of the set of next sequences of words that can show up (n-gram). The sequences with highest conditional probabilities can show up as top candidates.

To further improve this algorithm,

we can put more weight on past sequences which showed up more recently and near your location to account for trends

show your recent searches given partial data

Based on frequency and amount of donations, graduation year, major, etc, construct a supervised regression (or binary classification) algorithm.

Based on the past pickup location of passengers around the same time of the day, day of the week (month, year), construct

Ask someone for more details.

Based on the number of past pickups

account for periodicity (seasonal, monthly, weekly, daily, hourly)

special events (concerts, festivals, etc.) from tweets

One vector each for team A and B. Take the difference of the two vectors and use that as an input to predict the probability that team A would win by training the model. Train the models using past tournament data and make a prediction for the new tournament by running the trained model for each round of the tournament

Some extensions:

Experiment with different ways of consolidating the 2 team vectors into one (e.g concantenating, averaging, etc)

Consider using a RNN type model that looks at time series data.

This is equivalent to making the model more robust to outliers. [message type=”simple” bg_color=”#eeeeee” color=”#333333″]Probability[/message]

Naïve Bayes assumption tells that all independent variables are equally important as well

independent of each other. The reality doesn’t support this idea much. But surprisingly Naïve Bayes

model sometimes works efficient for classification problem.

p=1/4+1/4p+1/2p^2 => p=1/2

1-(0.8)^4. Or, we can use Poisson processes

Uniform Distribution is identified when the data spread is equal in the range. Right/Left skewed data

is something if data is distributed on any of one side of the plot.

Flip twice and if HT then H, TH then T.

more than two standard deviations

plug in the value to the CDF of the same random variable

1/3

gender ratio is 1:1. Expected number of children is 2. let X be the number of children until getting a female (happens with prob 1/2). this follows a geometric distribution with probability 1/2

the outcome follows a multinomial distribution with n=12 and k=3. but the classes are indistinguishable

the probability of a hash collision: 1-(10!/10^10)

the expected number of hash collisions: 1-10*(9/10)^10

the expected number of hashes that are unused: 10*(9/10)^10

Lyfts arrive first: 2!*3!/5!

Ubers arrive first: same

100+60-20=140

24C5*(1+5(24-5))/24C5*24C5 = 4/1771

1

Shorter. Regression to the mean

the expected number of coin flips until you get two tails in a row.

less than $3

4/13 [message type=”simple” bg_color=”#eeeeee” color=”#333333″]Data Analysis[/message]

collaborative filtering

goodness of fit measure. variance explained by the regression / total variance

the more predictors you add the higher R^2 becomes.

hence use adjusted R^2 which adjusts for the degrees of freedom

or train error metrics

High dimensionality makes clustering hard, because having lots of dimensions means that everything is “far away” from each other.

For example, to cover a fraction of the volume of the data we need to capture a very wide range for each variable as the number of variables increases

All samples are close to the edge of the sample. And this is a bad news because prediction is much more difficult near the edges of the training sample.

The sampling density decreases exponentially as p increases and hence the data becomes much more sparse without significantly more data.

We should conduct PCA to reduce dimensionality

Statistically,

It depends on the quality of your data, for example, if your data is biased, just getting more data won’t help.

It depends on your model. If your model suffers from high bias, getting more data won’t improve your test results beyond a point. You’d need to add more features, etc.

Practically,

Also there’s a tradeoff between having more data and the additional storage, computational power, memory it requires. Hence, always think about the cost of having more data.

Data sets have errors. You won’t find them all but you might find some. That 212 year old man. That 9 foot tall woman.

Variables can have skewness, outliers etc. Then the arithmetic mean might not be useful. Which means the standard deviation isn’t useful.

Variables can be multimodal! If a variable is multimodal then anything based on its mean or median is going to be suspect.

Proper exploratory data analysis.

In every data analysis task, there’s the exploratory phase where you’re just graphing things, testing things on small sets of the data, summarizing simple statistics, and getting rough ideas of what hypotheses you might want to pursue further.

Then there’s the exploitatory phase, where you look deeply into a set of hypotheses.

The exploratory phase will generate lots of possible hypotheses, and the exploitatory phase will let you really understand a few of them. Balance the two and you’ll prevent yourself from wasting time on many things that end up meaningless, although not all.

data analysis is a repetition of setting up a new hypothesis and trying to refute the null hypothesis.

The scientific method is eminently inductive: we elaborate a hypothesis, test it and refute it or not. As a result, we come up with new hypotheses which are in turn tested and so on. This is an iterative process, as science always is.

run the features though a Gradient Boosting Machine or Random Forest to generate plots of relative importance and information gain for each feature in the ensembles.

Look at the variables added in forward variable selection

Remove rows with missing values – This works well if 1) the values are missing randomly (see Vinay Prabhu’s answer for more details on this) 2) if you don’t lose too much of the dataset after doing so.

Build another predictive model to predict the missing values – This could be a whole project in itself, so simple techniques are usually used here.

Use a model that can incorporate missing data – Like a random forest, or any tree-based method.

Multicollinearity refers to a situation in which two or more explanatory variables in a multiple regression model are highly linearly related.

Leave the model as is, despite multicollinearity. The presence of multicollinearity doesn’t affect the efficiency of extrapolating the fitted model to new data provided that the predictor variables follow the same pattern of multicollinearity in the new data as in the data on which the regression model is based.

principal component regression

PCA

ridge / lasso / elastic net regression

Univariate Feature Selection where a statistical test is applied to each feature individually. You retain only the best features according to the test outcome scores

“Recursive Feature Elimination”:

First, train a model with all the feature and evaluate its performance on held out data.

Then drop let say the 10% weakest features (e.g. the feature with least absolute coefficients in a linear model) and retrain on the remaining features.

Iterate until you observe a sharp drop in the predictive accuracy of the model.

p > n.

If some of the explanatory variables are perfectly correlated (positively or negatively) then the coefficients would not be unique.

The dataset might be heterogeneous. In which case, it is recommended to cluster datasets into different subsets wisely, and then draw different models for different subsets. Or, use models like non parametric models (trees) which can deal with heterogeneity quite nicely.

What is the main idea behind ensemble learning? If I had many different models that predicted the same response variable, what might I want to do to incorporate all of the models? Would you expect this to perform better than an individual model or worse?

The assumption is that a group of weak learners can be combined to form a strong learner.

Hence the combined model is expected to perform better than an individual model.

Assumptions:

average out biases

reduce variance

Bagging works because some underlying learning algorithms are unstable: slightly different inputs leads to very different outputs. If you can take advantage of this instability by running multiple instances, it can be shown that the reduced instability leads to lower error. If you want to understand why, the original bagging paper( http://www.springerlink.com/cont…) has a section called “why bagging works”

Boosting works because of the focus on better defining the “decision edge”. By reweighting examples near the margin (the positive and negative examples) you get a reduced error (see http://citeseerx.ist.psu.edu/vie…)

Use the outputs of your models as inputs to a meta-model.

For example, if you’re doing binary classification, you can use all the probability outputs of your individual models as inputs to a final logistic regression (or any model, really) that can combine the probability estimates.

One very important point is to make sure that the output of your models are out-of-sample predictions. This means that the predicted value for any row in your dataframe should NOT depend on the actual value for that row.

If the data is more used in one room, then that one is over utilized! Maybe account for the room capacity and normalize the data.

like page rank with each user corresponding to the web pages and linking to the page equivalent to following.

One way you could do this is by storing a “skill level” for each user and a “difficulty level” for each problem. We assume that the probability that a user solves a problem only depends on the skill of the user and the difficulty of the problem.* Then we maximize the likelihood of the data to find the hidden skill and difficulty levels.

The Rasch model for dichotomous data takes the form:

{\displaystyle \Pr\{X_{ni}=1\}={\frac {\exp({\beta _{n}}-{\delta _{i}})}{1+\exp({\beta _{n}}-{\delta _{i}})}},}

where is the ability of person and is the difficulty of item}.

Some people would take the mean rank of each sushi. If I wanted something simple, I would use the median, since ranks are (strictly speaking) ordinal and not interval, so adding them is a bit risque (but people do it all the time and you probably won’t be far wrong).

collaborative filtering. you have your votes and we can calculate the similarity for each representatives and select the most similar representative

for liberal and republican parties, find the mean vector and find the representative closest to the center point

reduce the text to a more compact form (e.g. fingerprinting,

bag of wor

ds) then compare those with other texts by calculating the similarity

KNN

choose a small value of k that still has a low SSE (elbow method)

https://bl.ocks.org/rpgove/0060ff3b656618e9136b

Statistical Inference

Plot the distributions of multiple features for both A and B and make sure that they have the same shape. More rigorously, we can conduct a permutation test to see if the distributions are the same.

MANOVA to compare different means

Verify the sampling algorithm is random.

The user might not act the same suppose had they not seen the other bucket. You are essentially adding additional variables of whether the user peeked the other bucket, which are not random across groups.

Same as the previous question. The above problem can happen in larger scale.

Ask someone for more details.

one control, 20 treatment, if the sample size for each group is big enough.

Ways to attempt to correct for this include changing your confidence level (e.g. Bonferroni Correction) or doing family-wide tests before you dive in to the individual metrics (e.g. Fisher’s Protected LSD).

lower the variability by modifying the KPI

cap values

percentile metrics

log transform

https://www.quora.com/How-would-you-run-an-A-B-test-if-the-observations-are-extremely-right-skewed

exclusive -> ok

type-1 error: rejecting Ho when Ho is a true

type-2 error: not rejecting Ho when Ha is true

Q49. You are AirBnB and you want to test the hypothesis that a greater number of photographs increases the chances that a buyer selects the listing. How would you test this hypothesis?

For randomly selected listings with more than 1 pictures, hide 1 random picture for group A, and show all for group B. Compare the booking rate for the two groups.

Ask someone for more details.

The best way I know to quantify the impact of performance is to isolate just that factor using a slowdown experiment, i.e., add a delay in an A/B test.

A method for parameter optimization (fitting a model). We choose parameters so as to maximize the likelihood function (how likely the outcome would happen given the current data and our model).

maximum likelihood estimation (MLE) is a method of estimating the parameters of a statistical model given observations, by finding the parameter values that maximize the likelihood of making the observations given the parameters. MLE can be seen as a special case of the maximum a posteriori estimation (MAP) that assumes a uniform prior distribution of the parameters, or as a variant of the MAP that ignores the prior and which therefore is unregularized.

for Gaussian mixtures, non-parametric models, it doesn’t exist

MAP estimates the posterior distribution given the prior distribution and data which maximizes the likelihood function. MLE is a special case of MAP where the prior is uninformative uniform distribution.

MOM sets moment values and solves for the parameters. MOM has not used much anymore because maximum likelihood estimators have higher probability of being close to the quantities to be estimated and are more often unbiased.

For example, 95% confidence interval is an interval that when constructed for a set of samples each sampled in the same way, the constructed intervals include the true mean 95% of the time.

if confidence intervals are constructed using a given confidence level in an infinite number of independent experiments, the proportion of those intervals that contain the true value of the parameter will match the confidence level.

Unbiasedness means that the expectation of the estimator is equal to the population value we are estimating. This is desirable in inference because the goal is to explain the dataset as accurately as possible. However, this is not always desirable for data analysis or predictive modeling as there is the bias variance tradeoff. We sometimes want to prioritize the generalizability and avoid overfitting by reducing variance and thus increasing bias.

OTHER Important Data Science Interview Questions and Answers

Sample is the set of people who participated in your study whereas the population is the set of people to whom you want to generalize the results. For example – If you want to study the obesity among the children in India and you study 1000 children then those 1000 became sample whereas the all the children in the country is the population.

Sample is the subset of population.

Sample frame is the number of people who wanted to study whereas sample is the actual number of people who participated in your study. Ex – If you sent a marketing survey link to 300 people through email and only 100 participated in the survey then 300 is the sample survey and 100 is the sample.

Sample is the subset of sample frame. Both Sample and Sample Frame are subset of population.

Univariate analysis is performed on one variable, bivariate on two variable and multivariate analysis on two or more variables

Extrapolation is the estimation of future values based on the observed trend on the past. Interpolation is the estimation of missing past values within two values in a sequence of values

Precision is the percentage of correct predictions you have made and recall is the percentage of predictions that actually turned out to be true

- Confusion matrix is a table which contains information about predicted values and actual values in a classification model
- It has four parts namely true positive ,true negative, false positive and false negative
- It can be used to calculate accuracy, precision and recall

While performing the an experiment hypothesis testing to is used to analyze the various factors that are assumed to have an impact on the outcome of experiment

An hypothesis is some kind of assumption and hypothesis testing is used to determine whether the stated hypothesis is true or not

Initial assumption is called null hypothesis and the opposite alternate hypothesis

In hypothesis testing, p value helps to arrive at a conclusion. When p -value is too small then null hypothesis is rejected and alternate is accepted. When p-value is large then null hypothesis is accepted.

Type-I error is we reject the null hypothesis which was supposed to be accepted. It represents false positive

Type-II error represents we accept the null hypothesis which was supposed to be rejected. It represents false negative.

- Deletion of values
- Guess the value
- Average Substitution
- Regression based substitution
- Multiple Imputation

When building a statistical model the objective is reduce the value of the cost function that is associated with the model. Gradient descent is an iterative optimization technique used to determine the minima of the cost function

Supervised learning are the class of algorithms in which model is trained by explicitly labelling the outcome. Ex. Regression, Classification

Unsupervised learning no output is given and the algorithm is made to learn the outcomes implicity Ex. Association, Clustering

Regularization is used to penalize the model when it overfits the model. It predominantly helps in solving the overfitting problem.

High Bias is an underlying error wrong assumption that makes the model to underfit. High Variance in a model means noise in data has been too taken seriously by the model which will result in overfitting.

Typically we would like to have a model with low bias and low variance

- Introduce Regularization
- Perform Cross Validation
- Reduce the number of features
- Increase the number of entries
- Ensembling

When you build a model which has very high model accuracy on train data set and very low prediction accuracy in test data set then it is a indicator of overfitting

Elbow method ( Plotting the percentage of variance explained w.r.t to number of clusters)

Gap Statistic

Silhouette method

Correlation is the measure that helps us understand the relationship between two or more variables

Causation represents that causal relationship between two events. It is also known to represent cause and effect

Causation means there is correlation but correlation doesn’t necessarily mean causation

Normal distribution is a bell shaped curve that represents distribution of data around its mean. Any normal process would follow the normal distribution.

Most of data points tend to concentrated around the mean. If a point is further away from the mean then it is less likely to appear

Group by function

Pivot function

Aggregate function

List a = [1,2,3,4] List b= [1,2,5,6] A = list(set(a+b))

By using a library called pickle you can train any model and store the object in a pickle file.

When needed in future you can retrieve the object and use the model for prediction.

Anomaly detection is identification of items or events that didn’t fit to the exact pattern or other items in a dataset. Outliers are valid data points that are outside the norm whereas anomaly are invalid data points that are created by process that is different from process that created the other data points

Ensemble learning is the art of combining more than one model to predict the final outcome of an experiment. Commonly used ensemble techniques bagging, boosting and stacking

Numpy

Scipy

Pandas

Scikit learn

Matplotlib\ seaborn

Data is broadly classified into two types 1) Numerical 2) Categorical

Numerical variables is further classified into discrete and continuous data

Categorical variables

Systematic Sampling

Stratified Sampling

Quota Sampling are further classified into Binary, Nominal and Ordinal data

Lambda function are used to create small, one-time anonymous function in python. It enables the programmer to create functions without a name and almost instantly

- Random Sampling
- Systematic Sampling
- Stratified Sampling
- Quota Sampling

- Missing Values
- Noise in the Data Set
- Outliers
- Mixture of Different Languages (like English and Chinese)
- Range Constraints

Supervised learning: Target variable is available and the algorithm learns for the train data

And applies to test data (unseen data).

Unsupervised learning: Target variable is not available and the algorithm does not need to learn

Anything beforehand.

- Fraud detection
- Disease screening

Imbalanced Data Set means that the population of one class is extremely large than the other

(Eg: Fraud – 99% and Non-Fraud – 1%)

Imbalanced dataset can be handled by either oversampling, undersampling and penalized Machine Learning Algorithm.

- Machine learning algorithmsuits well for small data and it might take huge amount of time to train for large data.
- Whereas Deep learning algorithm takes less amount of data to train due to the help of GPU(Parallel Processing).

- Linear Regression and Logistic Regression
- Decision Trees and Random Forest
- SVM
- Naïve Bayes
- XGBoost

Apply step function, which calculates the AIC for different permutation and combination of features and provides the best features for the dataset.

Feature engineering is the process of using domain knowledge of the data to create features for machine learning algorithm to work

- Adding more columns (or) removing columns from the existing column
- Outlier Detection
- Normalization etc

- In Logistic Regression, we can use step() which gives AIC score of set of features
- In Decision Tree, We can use information gain(which internally uses entropy)
- In Random Forest, We can use varImpPlot

It exists when 2 or more predictors are highly correlated with each other.

Example: In the Data Set if you have grades of 2^{nd} PUC and marks of 2^{nd} PUC, Then both gives the same trend to capture, which might internally hamper the speed and time.so we need to check if the multi collinearity exists by using VIF(variance Inflation Factor).

Note: if the Variance Inflation Factor is more than 4, then multi collinearity problem exists.

Measure how much the variance of the estimated regression coefficients are inflated as compared to when the predictor variables are not linearly related.

- Parametric machine learning algorithm– Linear Regression, Logistic Regression
- Non-Parametric machine learning algorithm – Decision Trees, SVM, Neural Network

Algorithm which does not make strong assumptions are non-parametric algorithm and they are free to learn from training data. Algorithm that makes strong assumptions are parametric and it involves

- select the form for the function and
- learn the coefficients for the function from training data.

It works better when we remove the attributes which are unrelated to the output variable and highly co-related variable to each other.

Reason: It assumes that the input variable is independent, but in real world it is unrealistic, since all the features would be dependent on each other.

- False Positive – A cancer screening test comes back positive, but you don’t have cancer
- False Negative – A cancer screening test comes back negative, but you have cancer
- True Positive – A Cancer Screening test comes back positive, and you have cancer
- True Negative – A Cancer Screening test comes back negative, and you don’t have cancer

Sensitivity means “proportion of actual positives that are correctly classified” in other words “True Positive”

Specificity means “proportion of actual negatives that are correctly classified” “True Negative”

If you are dealing with a classification problem like (Yes/No, Fraud/Non Fraud, Sports/Music/Dance) then use Logistic Regression.

If you are dealing with continuous/discrete values, then go for Linear Regression.

Imputation algorithm means “replacing the Blank values by some values)

- Mean imputation
- Median Imputation
- MICE
- miss forest
- Amelia

The analogous metric of adjusted R² in logistic regression is AIC.

AIC is the measure of fit which penalizes model for the number of model coefficients. Therefore, we always prefer model with minimum AIC value.

E(S) = 8/10log(8/10) – 2/10log(2/10)

Note: Log is à base 2

In Machine Learning. Perceptron is an algorithm for supervised classification of the input into one of several possible non-binary outputs

- Keep the attributes/Columns which are really important
- Use K-Fold cross validation techniques
- Make use of drop-put incase of neural network

Mathematical Formula “Entropy” is utilized for predicting the root node of the tree.

- TensorFlow
- Theano
- CNTK

- TensorFlow
- Theano
- Lasagne
- mxnet
- blocks
- Keras
- CNTK
- TFLearn

Using Stratified Shuffle package

It means that “traversing the data set one time

Ensemble Model is a combination of Different Models to predict correctly and with good accuracy.

Ensemble learning is used when you build component classifiers that are more accurate and independent from each other.

- SVM can be used if the data is outlier free whereas Naïve Bayes can be used even if it has outliers (since it has built in package to take care).
- SVM suits best for Text Classification Model and Random Forest suits for Binomial/Multinomial Classification Problem.

- Random Forest takes care of over fitting problem with the help of tree pruning

- Self Driving Cars
- Image Classification
- Text Classification
- Search Engine
- Banking, Healthcare Domain

Logistic Regression

Linear Regression

Bayes Theorem

If you want all core processors in your system to be utilized, then go for XGBoost(since it supports parallel processing) and if your data is small then go for random forest.

Overfitting.

Overfitting and can be reduced by many methods like (Tree Pruning, Removing the minute information provided in the data set).

This kind of recommendation engine comes from collaborative filtering.

- Margin – Distance between the hyper plane and closest data points is referred as “margin”
- Kernels – there are three types of kernel which determines the type of data you are dealing with i) Linear, ii) Radial, iii) Polynomial
- Regularization – The Regularization parameter (often termed as C parameter in python’s sklearn library) tells the SVM optimization how much you want to avoid misclassifying each training example

Boosting is a Ensemble technique that attempts to create strong classifier from a number of weak classifiers

- After the first tree is created, the performance of the tree on each training instance is used to weight how much attention the next tree that is created should pay attention to each training instance by giving more weights to the misclassified one.
- Models are created one after the other, each updating the weights on the training instance

Null Deviance indicates the response predicted by a model with nothing but an intercept

Residual deviance indicates the response predicted by a model on adding independent variables

Note:

Lower the value, better the model

Information gain and gini index

Not suitable for continuous/Discrete variable

Performs poorly on small data

These are important feature extraction techniques used for dimensionality reduction.

- Calculate the Accuracy only? (or)
- Precision, Recall, F1 Score separately

We need to calculate precision, Recall separately

- Keep the attributes/Columns which are really important
- Use K-Fold cross validation techniques
- make use of drop-put in case of neural network

Step 1:- How to find the Root Node

Use Information gain to understand the each attribute information w.r.t target variable and place the attribute with the highest information gain as root node.

Step 2:- How to Find the Information Gain

Please apply the entropy (Mathematical Formulae) to calculate Information Gain. Gain (T,X) = Entropy(T) – Entropy(T,X) here represent target variable and X represent features.

Step3: Identification of Terminal Node

Based on the information gain value obtained from the above steps, identify the second most highest information gain and place it as the terminal node.

Step 4: Predicted Outcome

Recursively iterate the step4 till we obtain the leaf node which would be our predicted target variable.

Step 5: Tree Pruning and optimization for good results

It helps to reduce the size of decision trees by removing sections of the tree to avoid over fitting.

It is a line that splits the input variable space and it is selected to best separate the points in the input variable space by their class(0/1,yes/no).

Eg: I Love Data Science

Bigram – (I Love) (Love Data) (Data Science)

Relu, Leaky Relu , Softmax, Sigmoid

SVM, Naïve Bayes, Keras, Theano, CNTK, TFLearn(Tensorflow)

- Principal Component Analysis(PCA) would help us here which can explain the maximum variance in the data set.
- We can also check the co-relation for numerical data and remove the problem of multi-collinearity(if exists) and remove some of the columns which may not impact the model.
- We can create multiple dataset and execute them batch wise.

Accuracy of 96% is good. But we may have to check the following items:

- what was the dataset for the classification problem
- Is Sensitivity and Specificity are acceptable
- if there are only less negative cases, and all negative cases are not correctly classified, then it might be a problem

In-Addition it is related to fraud detection, hence needs to be careful here in prediction (i.e not wrongly predicting the fraud as non-fraud patient.

Prior probability:

The proportion of dependent variable in the data set.

Likelihood:

It is the probability of classifying a given observation as ‘1’ in the presence of some other variable.

Q154. How can we know if your data is suffering from low bias and high variance?” open=”no” style=”default” icon=”plus” anchor=”” class=””]

Random Forest Algorithm can be used to tackle high variance problem.in the cases of low bias and high variance L1,L2 regularization can help.

Kmeans partitions a data set into clusters, which is homogeneous and points in the cluster are close to each other. Whereas KNN tries to classify unlabelled observation based on its K surrounding neighbours.

It is the classical example of over fitting. It is not performing well on the unseen data. We may have to tune our model using cross validation and other techniques to overcome over fitting

We can remove them, if it does not impact our model

We can apply imputation techniques (like MICE, MISSFOREST,AMELIA) to avoid missing values

Type I error occurs when – “we classify a value as positive, when the actual value is negative”

(False Positive)

Type II error occurs when – “we classify a value as negative, when the actual value if positive”

(False Negative)

- If it is classification related problem,then we can use logistic,decision trees etc…
- If it is Regression related problem, then we can use Linear Regression.
- If it is Clustering based, we can use KNN.
- We can also apply XGB, RF for better accuracy.

Data Set can have one column in the range (10,000/20,000) and other column might have data in the range (1, 2, 3).clearly these two columns are in different range and cannot accurately analyse the trend. So we can apply normalization here by using min-max normalization (i.e to convert it into 0-1 scale).

Formally, It’s the way to Quantify your intuitions.

Technically, Data Science is a combination of Machine Learning, Deep Learning & Artificial

Intelligence. Where Deep Learning is the subset of AI.

Machine learning is the process of generating the predictive power using past data(memory). It is a

one-time process where the predictions can fail in the future (if your data distribution changes).

Deep Learning is the process of adding one more logic to the machine learning, where it iterates

itself with the new data and will not fail in future, even though your data distribution changes. The

more it iterates, more it works better.

R can be used whenever the data is structed. Python is efficient to handle unstructured data. R can’t

handle high volume data. Python backend working with Theano/tensor made it easy to perform it as

fast comparing with R.

Logistic Regression, KNN, Random Forest, CART, C50 are few algorithms which can perform Binary

classification.

Naïve Bayes, Random Forest are widely used for multinomial classification.

LOGIT function is Log of ODDS ratio. ODDS ratio can be termed as the Probability of success divided

by Probability of failure. Which is the final probability value of your binary classification, where we

use ROC curve to get the cut-Off value of the probability.

• Structural Analysis

• Outlier Analysis

• Missing value treatments

• Feature engineering

Whenever data that defines with having Mean = Median = Mode, then the data is called as normally

distributed data.

Empirical Rule says that whenever data is normally distributed, your data should be having the

distribution in a way of,

68 percent of your data spread is within Plus or Minus 1 standard deviation

95 percent of your data spread is within Plus or Minus 2 standard deviation

99.7 percent of your data spread is within Plus or Minus 3 standard deviation

Q171. What is Regression problem statement?” open=”no” style=”default” icon=”plus” anchor=”” class=””]

With the help of Independent variables(X), we predict target variable(Y), if your target variable

having infinite possibilities, then the problem will fall under Regression problem statement.

Standard error metrics are RMSE & MAPE.

RMSE: Root Mean Squared Error (where we use least square values).

MAPE: Mean Absolute Percent Error (Here, we use absolute values).

R is the correlation coefficient. Which will be in the range of 0 to 1. If value is closer to 1, it means

that Independent variables are highly correlated to your target variable.

Can be given by the formula: (slope*standard deviation(X))/ standard deviation(Y)

An outlier is an observation that lies in an abnormal distance from other values. In a sense, this

definition leaves it up to the analyst (or a consensus process) to decide what will be considered

abnormal.

Example:data – (2,1,1,3,4,2,1,4,5,6,2,6,8,9,64,1,7,9)

Only one data point is not in the distribution. You could see all data points are within the

range of 1-9. But one data point has a value of 64. Which can be considered as an Influential data

point.

Box plot is the standard mechanism which can be used in the univariate Analysis.

Scatter plot can be used for Bi-variate Analysis.

Outliers should be to investigated first. Investigation should be in a way that, what is the reason

behind that outlier value? Is it possible to change those values by our investigations manually? If

can’t be treated manually, need to remove the observation if the values are highly deviated. If the

deviation is low, can keep the outliers as such and we can proceed.

Mean, Median & Mode can be always the better replacements.

• Central Imputations

• KNN Imputations

Upper Whisker: Q3 + 1.5(IQR)

Lower Whisker: Q1 – 1.5(IQR)

IQR: Inter-Quartile Range. Which is given by Q3 – Q1.

The default datatype is string. type(input()) will be string.

for i in range(10):

a=0

a+=i

print(a)

Ans: 9

j = ‘a’

For i in range(2):

j+=j

Ans: ‘aaaa’

L = ()

L.append(10)

Ans: Attribute error – tuple has no attribute append

a = [i+j for i,j in zip(range( 10),range(1,11))]

print(a) : class=””]

Ans: [1,3,5,7,9,11,13,15,17,19]

- A set has no duplicate entries, whereas a tuple can have duplicate values.
- Set is mutable, whereas tuple is immutable.

- fromkeys() is the function used to convert a list, set, tuple to a dictionary.
- The values from the list/set/tuple become the keys of the dictionary.

print([i for i in range(2,101) if i%2!=0])

prime = []

for i in range ( 2,101):

count= 0

for j in range(2,int((i**0.5)+1)):

if i%j==0:

count +=1

if count == 0:

prime.append(i)

print(prime)

a = 0

if a:

print(‘yes’)

else:

print(‘false’)

- ‘false’ – since 0 is interpreted as false
- What the output of the following code?

a = ‘hello ’

if a:

print(‘true’)

else:

print(‘false’)

Ans: ‘true’ – since any string value is interpreted as true.

Gradient descent algorithm is used to minimize the cost function of linear regression.

Gini Index or entropy can both be the cost function of decision tree algorithm.

Multinomial Naïve Bayes is used for classification of more than two classes.

We use feature selection to filter variables,which are not necessary for predication and not have

sufficient datas.By filtering the variables,we improve the performance of the` model. Some of the

feature selection techniques are wrapper methods,embedded methods and filter methods.

Three data structures.

1.Series : They are one dimensional array with heterogenous datatypes.

2.DataFrame : They are two dimensional,having two or more rows and columns.

3.Panel : Three dimensional data

Label encoder is used for converting categorical values into numerical values.Label encoder labels

the classes from 0 to n-classes -1. It is mainly used for categorical variables having two or more

different classes.

loc() is label-based while iloc() is index-based. loc() slices the particular data using row labels

and column labels ,while iloc() slices the particular data using row indexes and column indexes.

1.Forward feature selection is starts with no feature & adds one at a time.

2.Backward feature elimination is starts with all features present & removes one feature at the time.

3.Bi-directional elimination(Stepwise Selection) is a combination of both forward & backward feature

selection methods.

Yes.Dictionaries are ordered.They follow insertion order.This feature comes after python 3.6+.

Before that python dictionaries are unordered.However,in python 3.1 a feature “ordereddict” was

introduced to keeps the insertion order of the items.

Bagging classifier is a machine learning algorithm,it specifies results by having decision tree

as its base-estimator .Having max_samples as hyperparameter it allows number of samples used to

fit each decison tree.Thus,it aggregates each model by voting to obtain a final prediction .

Data Cleansing is the process of fixing/removing duplicates and inappropriate data from a

table/record/database.Steps involved in cleaning data are removing duplicates,fix structural

data,removing outliers and handling missing/incorrect data.It helps to improve the data

quality and quick decision-making.

Matplotlib

Plotly

Seaborn

GGplot

Altair

Bokeh

Pygal

Geoplotlib

Missingno

Leather

Outliers are data values which are distant from other observations.An outlier with extremely

high increases variability and affects mean which results incorrect output.

Standardization is a technique used in machine learning used to prevent large differences

between input values.We use StandardScalar in Scikit learn to transform input values with a

Gaussian distribution and differing means & standard deviations to a standard Gaussian

distribution with a mean of Zero and a standard deviation of One.

K-means clustering is one of the unsupervised learning algorithm comes under centroid-based

clustering algorithms.We partitioned set of points into K-groups .Each group is having a

centroid such that all points are having minimal distance from the centroid.

Confusion matrix is used to evaluate how a machine learning model is performing.It is table

of 2×2 matrix having actual values as columns and predicted values as rows in such a way that

it has true positive,true negative,false positive and false negative values.We need confusion

matrix to know our model’s accuracy,precison(how much we predict correctly in predicted

positive cases), recall and F1-score.

Nominal variables are also known as categorical variables which cannot be ordered.eg.sex,colors.

Ordinal variables are also known as categorical variables are those variables which can be ordered

from lowest to highest or with any special measurement.eg.growth stages of human.

Missing data reduce the model performance.We can handle missing data by removal of rows or

columns and some imputation techniques such as fill with zero, impute with mean , median or mode.

One hot encoding is used to convert categorical data into numerical data in the form of 0s

and 1s.It is the process of creating dummy variables.One hot encoding is maximum used for

categorical variables having two different classes.

R2 score is also known as coefficient of determination & it is calculated by,

R2 = 1- SSres / SStot

where,

SSres = the sum of squares of the residual errors.

SStot = the total sum of the errors.

R2 score is also known as coefficient of determination R2 score tells how

close our model fits with the actual data.It varies b/w 0 and 1. If r2

score is high means our model performance is good.

Linear regression is used to find the relationship b/w a independent variable(X)

& a dependent variable(Y) . linear regression can be done by fitting a linear equation

to observed data. A linear regression line has an equation of the shape

Y= mX + c

where,

Y = dependent variable

m = slope

X = independent variable

c = intercept for a given line.

1.Hierarchical Clustering methods (Algorithms- DIANA, AGNES, hclust etc.)

2.Partitioning methods (Algorithms – k-means, k-medians, k-modes)

3.Distribution-based Clustering methods (Algorithms- Gaussian Mixed Models, DBCLASD)

4.Density-based Clustering methods(Model-based methods)(Algorithms- DENCAST, DBSCAN)

5.Fuzzy Clustering methods(Algorithms- Fuzzy C Means, Rough k means)

6.Constraint Based Clustering methods(Algorithms- Decision Trees, Random Forest, Gradient Boosting)

Data Preprocessing is the process of converting raw data into an understandable,valuable data

which involves data cleaning,data transformation and data reduction.Data Preprocessing

is a data mining technique helps to obtain the quality data.

Corelation describes how two variables are related to each other.Increase or decrease in one

variable will affect the other.

Data Munging (also known as Data Wrangling) is the process which involves the cleaning and

structuring raw data and transforming it into a desired format which helps to analysis and

make quicker decisions.

Data Analysis is the process of collecting, cleaning, structuring and Analysing the raw data

to learn more about the data to make smarter decisions.

Data mining is the process of analysing and extracting information from raw data by uncovering

patterns and relationship from raw data which helps us to learn more about the dataset and

analyse the dataset in different ways.

Tracking patterns

Classification Analysis

Outlier detection/Anomaly

Association Rule Mining

Clustering Analysis

Regression Analysis

Prediction

Decision trees

Precision is how much we predict correctly in predicted

positive cases. Precision is calculated by,

Precision = TP/ (TP + FP)

where TP is the True positive and FP is the False Positive

Overfitting occurs when the trained data of the model is too close to the other data of the actual model.

Underfitting occurs when the trained data of the model is vary from the other data of the actual model.

Descriptive Analysis

Predictive Analysis

Diagnostic Analysis

Prescriptive Analysis

Qualitative Analysis

Quantitative Analysis

Recall is how much are predicted as positive in total positive cases.

Recall is calculated by,

Recall = TP/(TP + FN)

where

TP = True positive and FN = False Negative

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