Data Science with Python Certification Data Science with Python Feature Engineering Techniques 4

Question 1

What is the correct way to apply sklearn's StandardScaler inside a cross-validation loop to avoid data leakage?

Accepted Answer

Include the scaler in a Pipeline and pass the pipeline to cross_validate

Answer

Wrapping the scaler in a Pipeline ensures it is fit only on the training fold and then applied to the test fold during each cross-validation iteration.

Question 2

Which technique encodes high-cardinality categorical features into a fixed-length binary vector using a hash function?

Accepted Answer

Feature hashing (hashing trick)

Answer

Feature hashing maps categories to indices via a hash function, producing a fixed-size sparse vector regardless of the number of unique categories.

Question 3

In feature engineering, what is 'weight of evidence' (WoE) encoding primarily used for?

Accepted Answer

Encoding categorical variables for binary classification

Answer

WoE encoding replaces categories with the log ratio of the proportion of events to non-events for that category, making it well-suited for logistic regression in binary classification.

Question 4

What issue arises when you apply PCA for dimensionality reduction before splitting data into train and test sets?

Accepted Answer

PCA components depend on the test set, causing data leakage

Answer

Fitting PCA on the full dataset before splitting leaks test-set variance information into the transformation, invalidating the holdout evaluation.

Question 5

Which pandas function is most efficient for creating multiple aggregated features from a GroupBy object in a single pass?

Accepted Answer

GroupBy.agg()

Answer

GroupBy.agg() accepts a dictionary or list of aggregation functions and computes all specified statistics in one pass, returning a summarized DataFrame.

Data Science with Python Certification Practice Test

Data Science with Python Certification Practice Test

Data Science with Python Certification Data Science with Python Feature Engineering Techniques 4