Expanding window operations in Pandas - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an expanding window operation in pandas?

An expanding window operation calculates a statistic over all data points from the start up to the current point, growing the window size as it moves forward.

beginner

How do you create an expanding window object in pandas?

Use the expanding() method on a pandas Series or DataFrame, for example: df.expanding().

intermediate

What is the difference between rolling and expanding window operations?

Rolling windows use a fixed-size window that moves forward, while expanding windows start at the beginning and grow larger with each step.

beginner

How can you calculate the expanding mean of a pandas Series named data?

Use data.expanding().mean() to get the mean of all values from the start up to each point.

intermediate

What does the min_periods parameter do in expanding window operations?

It sets the minimum number of observations required to have a valid result; before that, the result will be NaN.

Which pandas method creates an expanding window object?

A expanding()

B rolling()

C groupby()

D resample()

The expanding() method creates an expanding window object in pandas.

What does an expanding window operation compute at each step?

A Statistic over random samples

B Statistic over a fixed-size window

C Statistic over the last two points only

D Statistic over all data from start to current point

Expanding window operations compute statistics over all data from the start up to the current point.

What will data.expanding(min_periods=3).mean() return for the first two points?

A Mean values of first two points

B NaN values

C Zeros

D Errors

With min_periods=3, the first two points do not have enough data, so the result is NaN.

Which of these is NOT a valid aggregation function for expanding windows?

A max()

B sum()

C plot()

D mean()

plot() is not an aggregation function; it's used for visualization.

If you want a window that always includes the last 5 points only, which method should you use?

A rolling(window=5)

B expanding()

C cumsum()

D groupby()

The rolling(window=5) method creates a fixed-size window of 5 points.

Explain how expanding window operations work and give an example of when you might use them.

Think about how you track totals or averages that include all past data.

Describe the difference between expanding and rolling window operations in pandas.

Compare how the window size changes as you move through data.