Data Science with Python Certification Data Analysis with Python 2

Question 1

Which pandas method fills forward-propagates missing values along a column?

Accepted Answer

fillna(method='ffill')

Answer

ffill (forward fill) propagates the last valid observation forward to replace NaN values.

Question 2

What does df.pivot_table(values='sales', index='region', aggfunc='mean') return?

Accepted Answer

Mean sales value per region

Answer

pivot_table with aggfunc='mean' computes the mean of the values column grouped by the index.

Question 3

Which NumPy function stacks arrays vertically (row-wise)?

Accepted Answer

np.vstack

Answer

np.vstack stacks a sequence of arrays along the first (vertical) axis, equivalent to concatenate with axis=0.

Question 4

In pandas, what is the result of df.groupby('dept')['salary'].transform('mean')?

Accepted Answer

A Series with each row replaced by its department's mean salary

Answer

transform broadcasts the group-level aggregation back to the original DataFrame's shape.

Question 5

Which method converts a pandas Series of strings to datetime objects?

Accepted Answer

pd.to_datetime(Series)

Answer

pd.to_datetime() is the standard function for parsing strings or numbers into datetime objects.

Data Science with Python Certification Practice Test