Dunnhumby Data Scientist Interview Questions and Answers

1 hour aptitude test

Q1. What is one hot encoding
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Q1. What is your long term goal
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I was asked to write SQL queries for 3rd highest salary of the employee, some name filtering, group by tasks.
Python code to find the index of the maximum number without using numpy.

Q1. Explain the Project undertaken during the research and follow-up questions
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Q1. Write pandas query to separate the names as first and last name from the full name. Drop the duplicate columns and also the missing values. Write output for the Python code. Write SQL query to retrieve t...read more
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Answering questions related to data science concepts and techniques.
• Recall is the ratio of correctly predicted positive observations to the total actual positives. Precision is the ratio of correctly predicted positive observations to the total predicted positives.

• To reduce variance in an ensemble model, techniques like bagging, boosting, and stacking can be used. Bagging involves training multiple models on different ...read more
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Simple Aptitude questions, Data interpretation and verbal

Q1. Basic questions on Data Analytics, Projects mentioned
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Q2. Code in SQL and python(moderate)
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The candidate is asked to code in SQL and Python at a moderate level.
• Use SQL to query data from databases

• Use Python to manipulate and analyze data

• Practice writing SQL queries and Python scripts
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Q3. Machine Learning
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Q1. Questions related to python basics.
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Q2. Basic calculus to test math skills.
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Q3. Machine learning metrics.
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Q1. Policies, behavioral round.
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Q2. Work culture and the selection process.
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Q3. Discussion about previous employers and educational background.
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Sql, python, Statistics mcq, Aptitude test. These were medium level questions.

Q1. SQL and python, time complexity
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Q2. Make 2 lists a=[1,2,3,4] b=[9,8,5,5,2,3,3,4,1,1,10,9,2,3,4,10,10,9,7,7,8] Write a program to remove duplicate of b and keep only those elements of b which are not present in a, and the final list should ...read more
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Remove duplicates from list b, keep elements not in list a, and sort in ascending order.
• Create a set from list b to remove duplicates

• Use list comprehension to keep elements not in list a

• Sort the final list in ascending order
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Q3. SQL question Remove duplicate from a table tab1
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Use the DISTINCT keyword in SQL to remove duplicates from a table.
• Use the SELECT DISTINCT statement to retrieve unique rows from the table.

• Identify the columns that should be used to determine uniqueness.

• Example: SELECT DISTINCT column1, column2 FROM tab1;
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Given 2 case studies on data science and asked different possibilities to improve the models.

How to work with imbalance dataset.
How to remove null values, what is features engineering.
What is PCA
What is the working of XGBOOST

Q1. What was last project, tell me in detail. There were different technical questions related to my project
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