MS-DS Master of Data science MS-DS Master of Data science Data Wrangling and Preprocessing Questions and Answers 3

Question 1

When merging two datasets with a many-to-many relationship on the join key, what is the most critical preprocessing step?

Accepted Answer

Deduplicating or reshaping one dataset to establish a clear one-to-many relationship

Answer

Many-to-many joins produce a Cartesian product of matching rows, so deduplicating or reshaping ensures the merged result has the intended granularity.

Question 2

Which encoding strategy is most appropriate for a categorical variable with a natural ordering such as education level?

Accepted Answer

Ordinal encoding that preserves the rank order

Answer

Ordinal encoding assigns integers that reflect the inherent order of categories, preserving the ranking information that other encoding methods would discard.

Question 3

What problem does target encoding introduce that requires careful mitigation through cross-validation or smoothing?

Accepted Answer

Data leakage from the target variable into the features

Answer

Target encoding replaces categories with the mean of the target, which can leak target information into features and cause overfitting without proper regularization.

Question 4

During text data preprocessing for a data science pipeline, what is the correct order of operations?

Accepted Answer

Lowercasing, tokenization, stop word removal, stemming or lemmatization

Answer

The standard NLP preprocessing pipeline normalizes case first, splits text into tokens, removes uninformative stop words, and then reduces words to their base forms.

Question 5

What is the primary risk of applying feature scaling before splitting data into training and test sets?

Accepted Answer

Information from the test set leaks into the training set through shared scaling parameters

Answer

Fitting the scaler on the entire dataset before splitting allows test set statistics to influence training data transformation, constituting data leakage.

MS-DS Master of Data science Practice Test

MS-DS Master of Data science Practice Test

MS-DS Master of Data science MS-DS Master of Data science Data Wrangling and Preprocessing Questions and Answers 3