Preparing for a data science interview can be challenging, given the breadth of topics covered. At GFK, a leading market research firm, you can expect questions spanning Python, SQL, Machine Learning, Statistics, and Excel. Here’s a comprehensive guide to help you prepare, featuring key questions and concise answers for each topic.
Table of Contents
Python Interview Questions
Question: How does Python manage memory?
Answer: Python uses a private heap space for memory management, handled by the Python memory manager. It includes an in-built garbage collector to reclaim unused memory.
Question: What are Python decorators and how do they work?
Answer: Decorators are functions that modify the behavior of other functions or methods. They are applied using the @decorator_name syntax above a function definition.
Question: What is the difference between a list and a tuple in Python?
Answer: Lists are mutable, allowing modification after creation, while tuples are immutable and cannot be changed once defined. Lists use square brackets [], and tuples use parentheses ().
Question: Explain list comprehension with an example.
Answer: List comprehension is a concise way to create lists. Example: [x**2 for x in range(10)] generates a list of squares from 0 to 9.
Question: **What are *args and kwargs?
Answer: *args allows a function to accept any number of positional arguments, while **kwargs allows a function to accept any number of keyword arguments.
Question: What is a lambda function?
Answer: A lambda function is an anonymous, small, and single-line function defined using the lambda keyword. Example: lambda x: x + 1.
Question: How do you handle exceptions in Python?
Answer: Exceptions are handled using try, except, else, and finally blocks. Code in the try block is executed, and exceptions are caught in the except block.
SQL Interview Questions
Question: What is the difference between DELETE and TRUNCATE?
Answer: DELETE removes rows based on a condition and can be rolled back, while TRUNCATE removes all rows from a table, is faster, and cannot be rolled back.
Question: What is a subquery?
Answer: A subquery is a query nested inside another query, used in SELECT, INSERT, UPDATE, or DELETE statements to provide results to the main query.
Question: What is a view in SQL?
Answer: A view is a virtual table based on the result set of an SQL query, containing rows and columns from one or more tables.
Question: What is a stored procedure?
Answer: A stored procedure is a prepared SQL code that can be saved and reused, allowing for modular SQL code and complex operations.
Question: What is the purpose of the GROUP BY clause?
Answer: The GROUP BY clause groups rows with the same values in specified columns into summary rows, often used with aggregate functions like COUNT, SUM, and AVG.
Question: What is the difference between WHERE and HAVING clauses?
Answer: WHERE filters rows before grouping, while HAVING filters groups after the GROUP BY clause is applied.
Question: What is ACID in the context of databases?
Answer: ACID stands for Atomicity, Consistency, Isolation, and Durability, ensuring reliable processing of database transactions.
Machine Learning Interview Questions
Question: What is a decision tree?
Answer: A decision tree is a model that makes decisions based on a series of questions about the features of the data, splitting the data into branches until reaching a decision node.
Question: What is gradient descent?
Answer: Gradient descent is an optimization algorithm used to minimize the loss function by iteratively moving toward the direction of the steepest descent as defined by the negative gradient.
Question: What is the purpose of feature scaling?
Answer: Feature scaling standardizes the range of independent variables, improving the performance of algorithms sensitive to the scale of data, such as gradient descent and k-nearest neighbors.
Question: What is regularization and why is it useful?
Answer: Regularization adds a penalty to the loss function to discourage complex models, reducing overfitting and improving generalization. Common methods include L1 (Lasso) and L2 (Ridge) regularization.
Question: What is a neural network?
Answer: A neural network is a series of algorithms that attempt to recognize underlying relationships in data by mimicking the human brain’s network of neurons, commonly used in deep learning.
Question: What is ensemble learning?
Answer: Ensemble learning combines multiple models to improve performance, reduce variance, and increase robustness. Techniques include bagging, boosting, and stacking.
Question: What is a support vector machine (SVM)?
Answer: A support vector machine (SVM) is a supervised learning model that finds the hyperplane best-separating data into classes by maximizing the margin between the nearest points of different classes.
Statistics Interview Questions
Question: What is a type I error and a type II error?
Answer: A type I error occurs when the null hypothesis is incorrectly rejected (false positive), while a type II error occurs when the null hypothesis is incorrectly accepted (false negative).
Question: What is a t-test?
Answer: A t-test is a statistical test used to compare the means of two groups to determine if they are significantly different from each other. It is commonly used when the sample sizes are small and the population standard deviation is unknown.
Question: What is ANOVA (Analysis of Variance)?
Answer: ANOVA is a statistical method used to compare the means of three or more groups to determine if at least one group’s mean is significantly different from the others. It helps identify if there are any statistically significant differences between the groups.
Question: What is a regression analysis?
Answer: Regression analysis is a statistical technique used to model and analyze the relationship between a dependent variable and one or more independent variables. It helps in predicting the dependent variable based on the values of the independent variables.
Question: What is a chi-square test?
Answer: A chi-square test is a statistical test used to determine if there is a significant association between categorical variables. It compares the observed frequencies in each category with the expected frequencies under the null hypothesis.
Question: What is the difference between parametric and non-parametric tests?
Answer: Parametric tests assume underlying statistical distributions (e.g., normal distribution) and are used when data meets these assumptions, while non-parametric tests do not assume specific distributions and are used when data does not meet parametric assumptions.
Excel Interview Questions
Question: How do you use the CONCATENATE function?
Answer: The CONCATENATE function combines text from multiple cells into one cell. Syntax: =CONCATENATE(text1, text2, …). Alternatively, use the & operator (e.g., =A1 & B1).
Question: What are Excel macros, and how do you create one?
Answer: Excel macros are sequences of instructions to automate repetitive tasks. To create a macro, go to the “Developer” tab, click “Record Macro,” perform the actions, and then stop recording.
Question: How do you protect a worksheet in Excel?
Answer: To protect a worksheet, go to the “Review” tab, click “Protect Sheet,” set a password, and select the actions that users are allowed to perform on the protected sheet.
Question: What is the IF function, and how is it used?
Answer: The IF function performs a logical test and returns one value if the condition is true and another if false. Syntax: =IF(logical_test, value_if_true, value_if_false).
Question: What is the purpose of the SUMIF function?
Answer: The SUMIF function adds up values in a range that meet a specific condition. Syntax: =SUMIF(range, criteria, [sum_range]).
Question: How do you split text into columns in Excel?
Answer: To split the text into columns, select the cells, go to the “Data” tab, click “Text to Columns,” choose the delimiter or fixed width, and follow the wizard to complete the process.
Conclusion
Preparing for a data science interview at GFK involves brushing up on various technical skills across Python, SQL, Machine Learning, Statistics, and Excel. By familiarizing yourself with these key questions and concise answers, you’ll be better equipped to demonstrate your knowledge and expertise during the interview. Good luck!
