Data Science & Machine Learning

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1. What are decorators in Python? Ans: Decorators are used to add some design patterns to a function without changing its structure. Decorators generally are defined before the function they are enhancing. To apply a decorator we first define the decorator function. Then we write the function it is applied to and simply add the decorator function above the function it has to be applied to. For this, we use the @ symbol before the decorator. 2. What is the ACID property in a database? The full form of ACID is atomicity, consistency, isolation, and durability. • Atomicity refers that if any aspect of a transaction fails, the whole transaction fails and the database state remains unchanged. • Consistency means that the data meets all validity guidelines. • Concurrency management is the primary objective of isolation. • Durability ensures that once a transaction is committed, it will occur regardless of what happens in between such as a power outage, fire, or some other kind of disturbance. 3. What is the meaning of KPI in statistics? KPI is an acronym for a key performance indicator. It can be defined as a quantifiable measure to understand whether the goal is being achieved or not. KPI is a reliable metric to measure the performance level of an organization or individual with respect to the objectives. An example of KPI in an organization is the expense ratio. 4. Explain One-hot encoding and Label Encoding. How do they affect the dimensionality of the given dataset? One-hot encoding is the representation of categorical variables as binary vectors. Label Encoding is converting labels/words into numeric form. Using one-hot encoding increases the dimensionality of the data set. Label encoding doesn’t affect the dimensionality of the data set. One-hot encoding creates a new variable for each level in the variable whereas, in Label encoding, the levels of a variable get encoded as 1 and 0.

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1. Can you explain how the memory cell in an LSTM is implemented computationally? The memory cell in an LSTM is implemented as a forget gate, an input gate, and an output gate. The forget gate controls how much information from the previous cell state is forgotten. The input gate controls how much new information from the current input is allowed into the cell state. The output gate controls how much information from the cell state is allowed to pass out to the next cell state. 2. What is CTE in SQL? A CTE (Common Table Expression) is a one-time result set that only exists for the duration of the query. It allows us to refer to data within a single SELECT, INSERT, UPDATE, DELETE, CREATE VIEW, or MERGE statement's execution scope. It is temporary because its result cannot be stored anywhere and will be lost as soon as a query's execution is completed. 3. List the advantages NumPy Arrays have over Python lists? Python’s lists, even though hugely efficient containers capable of a number of functions, have several limitations when compared to NumPy arrays. It is not possible to perform vectorised operations which includes element-wise addition and multiplication. They also require that Python store the type information of every element since they support objects of different types. This means a type dispatching code must be executed each time an operation on an element is done. 4. What’s the F1 score? How would you use it? The F1 score is a measure of a model’s performance. It is a weighted average of the precision and recall of a model, with results tending to 1 being the best, and those tending to 0 being the worst. 5. Name an example where ensemble techniques might be useful? Ensemble techniques use a combination of learning algorithms to optimize better predictive performance. They typically reduce overfitting in models and make the model more robust (unlikely to be influenced by small changes in the training data). You could list some examples of ensemble methods (bagging, boosting, the “bucket of models” method) and demonstrate how they could increase predictive power.

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1. What are Different Kernels in SVM? Linear kernel - used when data is linearly separable. Polynomial kernel - When you have discrete data that has no natural notion of smoothness. Radial basis kernel - Create a decision boundary able to do a much better job of separating two classes than the linear kernel. Sigmoid kernel - used as an activation function for neural networks. 2. What is Cross-Validation? Cross-validation is a method of splitting all your data into three parts: training, testing, and validation data. Data is split into k subsets, and the model has trained on k-1of those datasets. The last subset is held for testing. This is done for each of the subsets. This is k-fold cross-validation. Finally, the scores from all the k-folds are averaged to produce the final score. 3. List the different types of relationships in SQL. One-to-One - This can be defined as the relationship between two tables where each record in one table is associated with the maximum of one record in the other table. One-to-Many & Many-to-One - This is the most commonly used relationship where a record in a table is associated with multiple records in the other table. Many-to-Many - This is used in cases when multiple instances on both sides are needed for defining a relationship. Self-Referencing Relationships - This is used when a table needs to define a relationship with itself. 4. What Are the Data Types Supported in Tableau? Following data types are supported in Tableau: Text (string) values Date values Date and time values Numerical values Boolean values (relational only) Geographical values (used with maps) ENJOY LEARNING 👍👍

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1. What do you understand by the term silhouette coefficient? The silhouette coefficient is a measure of how well clustered together a data point is with respect to the other points in its cluster. It is a measure of how similar a point is to the points in its own cluster, and how dissimilar it is to the points in other clusters. The silhouette coefficient ranges from -1 to 1, with 1 being the best possible score and -1 being the worst possible score. 2. What is the difference between trend and seasonality in time series? Trends and seasonality are two characteristics of time series metrics that break many models. Trends are continuous increases or decreases in a metric’s value. Seasonality, on the other hand, reflects periodic (cyclical) patterns that occur in a system, usually rising above a baseline and then decreasing again. 3. What is Bag of Words in NLP? Bag of Words is a commonly used model that depends on word frequencies or occurrences to train a classifier. This model creates an occurrence matrix for documents or sentences irrespective of its grammatical structure or word order. 4. What is the difference between bagging and boosting? Bagging is a homogeneous weak learners’ model that learns from each other independently in parallel and combines them for determining the model average. Boosting is also a homogeneous weak learners’ model but works differently from Bagging. In this model, learners learn sequentially and adaptively to improve model predictions of a learning algorithm

1. What are the uses of using RNN in NLP? The RNN is a stateful neural network, which means that it not only retains information from the previous layer but also from the previous pass. Thus, this neuron is said to have connections between passes, and through time. For the RNN the order of the input matters due to being stateful. The same words with different orders will yield different outputs. RNN can be used for unsegmented, connected applications such as handwriting recognition or speech recognition. 2. How to remove values to a python array? Ans: Array elements can be removed using pop() or remove() method. The difference between these two functions is that the former returns the deleted value whereas the latter does not. 3. What are the advantages and disadvantages of views in the database? Answer: Advantages of Views: As there is no physical location where the data in the view is stored, it generates output without wasting resources. Data access is restricted as it does not allow commands like insertion, updation, and deletion. Disadvantages of Views: The view becomes irrelevant if we drop a table related to that view. Much memory space is occupied when the view is created for large tables. 4. How to create a calculated field in Tableau? Click the drop down to the right of Dimensions on the Data pane and select “Create > Calculated Field” to open the calculation editor. Name the new field and create a formula. ENJOY LEARNING 👍👍

Coding and Aptitude Round before interview Coding challenges are meant to test your coding skills (especially if you are applying for ML engineer role). The coding challenges can contain algorithm and data structures problems of varying difficulty. These challenges will be timed based on how complicated the questions are. These are intended to test your basic algorithmic thinking. Sometimes, a complicated data science question like making predictions based on twitter data are also given. These challenges are hosted on HackerRank, HackerEarth, CoderByte etc. In addition, you may even be asked multiple-choice questions on the fundamentals of data science and statistics. This round is meant to be a filtering round where candidates whose fundamentals are little shaky are eliminated. These rounds are typically conducted without any manual intervention, so it is important to be well prepared for this round. Sometimes a separate Aptitude test is conducted or along with the technical round an aptitude test is also conducted to assess your aptitude skills. A Data Scientist is expected to have a good aptitude as this field is continuously evolving and a Data Scientist encounters new challenges every day. If you have appeared for GMAT / GRE or CAT, this should be easy for you. Resources for Prep: For algorithms and data structures prep,Leetcode and Hackerrank are good resources. For aptitude prep, you can refer to IndiaBixand Practice Aptitude. With respect to data science challenges, practice well on GLabs and Kaggle. Brilliant is an excellent resource for tricky math and statistics questions. For practising SQL, SQL Zoo and Mode Analytics are good resources that allow you to solve the exercises in the browser itself. Things to Note: Ensure that you are calm and relaxed before you attempt to answer the challenge. Read through all the questions before you start attempting the same. Let your mind go into problem-solving mode before your fingers do! In case, you are finished with the test before time, recheck your answers and then submit. Sometimes these rounds don’t go your way, you might have had a brain fade, it was not your day etc. Don’t worry! Shake if off for there is always a next time and this is not the end of the world.

❓ Question 2: What is a z-score? 1. A standardized value that indicates the number of standard deviations an observation is from the mean. 2. The range between the highest and lowest values in a set of data. 3. A measure of the spread of a set of data. 4. A measure of central tendency of a set of data. ✅ Correct Response: 1 Explanation: In statistics, a z-score is a standardized value that indicates the number of standard deviations an observation is from the mean of a set of datIt is used to compare values from different normal distributions and to calculate probabilities. https://t.me/DataScienceInterviews

❓ Question 1: What is the difference between a population and a sample in statistics? 1. A population is a subset of a sample. 2. A sample is a subset of a population. 3. A population is a larger group, while a sample is a smaller group. 4. A sample is a group that is more representative than a population. ✅ Correct Response: 2 Explanation: In statistics, a population is the entire group of individuals, objects, or events that we are interested in studying, while a sample is a smaller subset of the population that is selected for study. Samples are often used when it is not feasible or practical to study the entire population https://t.me/DataScienceInterviews

1.How will you handle missing values in data? There are several ways to handle missing values in the given data- 1.Dropping the values 2.Deleting the observation (not always recommended). 3.Replacing value with the mean, median and mode of the observation. 4.Predicting value with regression 5.Finding appropriate value with clustering 2. What is SVM? Can you name some kernels used in SVM? SVM stands for support vector machine. They are used for classification and prediction tasks. SVM consists of a separating plane that discriminates between the two classes of variables. This separating plane is known as hyperplane. Some of the kernels used in SVM are – Polynomial Kernel Gaussian Kernel Laplace RBF Kernel Sigmoid Kernel Hyperbolic Kernel 3.What is market basket analysis? Market Basket Analysis is a modeling technique based upon the theory that if you buy a certain group of items, you are more (or less) likely to buy another group of items. 4.What is the benefit of batch normalization? The model is less sensitive to hyperparameter tuning. High learning rates become acceptable, which results in faster training of the model. Weight initialization becomes an easy task. Using different non-linear activation functions becomes feasible. Deep neural networks are simplified because of batch normalization. It introduces mild regularisation in the network.