Data Science FREE Data Science Data Wrangling and Preprocessing Questions and Answers 3

Question 1

What is the primary risk of using Min-Max scaling on a dataset before splitting into training and test sets?

Accepted Answer

It introduces data leakage because test set statistics influence the transformation

Answer

Fitting the scaler on the entire dataset before splitting causes data leakage because the minimum and maximum values from the test set influence the training data transformation.

Question 2

Which pandas method is most efficient for converting a wide-format DataFrame with repeated measurements into long format?

Accepted Answer

melt()

Answer

The melt() function unpivots a wide-format DataFrame into long format by converting column headers into row values under a new variable column.

Question 3

When dealing with a heavily right-skewed target variable in a regression task, which preprocessing step is most commonly applied?

Accepted Answer

Box-Cox or log transformation

Answer

Box-Cox and log transformations compress large values and spread small values, making the distribution more symmetric and helping linear models meet their normality assumptions.

Question 4

What is the purpose of using stratified sampling when splitting a dataset into training and test sets?

Accepted Answer

To maintain the same class distribution in both the training and test sets

Answer

Stratified sampling preserves the proportion of each class in both splits, which is critical for imbalanced datasets where random splitting could leave minority classes underrepresented in one set.

Question 5

Which approach is recommended for handling high-cardinality categorical features with hundreds of unique values?

Accepted Answer

Target encoding or frequency encoding

Answer

Target encoding replaces categories with the mean of the target variable for that category, while frequency encoding uses occurrence counts, both avoiding the dimensionality explosion of one-hot encoding.

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Data Science FREE Data Science Data Wrangling and Preprocessing Questions and Answers 3