Resetting index in Pandas - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the reset_index() method do in pandas?

It moves the current index of a DataFrame back into columns and resets the index to the default integer index starting from 0.

beginner

How do you keep the old index as a column when resetting the index in pandas?

By default, reset_index() keeps the old index as a new column. You can also use reset_index(drop=False) to explicitly keep it.

intermediate

What happens if you use reset_index(drop=True) in pandas?

The old index is removed completely and not added as a column. The DataFrame gets a new default integer index.

beginner

Why might you want to reset the index of a DataFrame?

To clean up the DataFrame after filtering or sorting, or before saving/exporting, so the index is simple and sequential starting at 0.

intermediate

Can reset_index() be used on a DataFrame with a MultiIndex?

Yes, it will move all levels of the MultiIndex into columns and reset the index to default integers.

What is the default behavior of df.reset_index() in pandas?

A Moves the index to columns and resets index to integers

B Deletes the DataFrame

C Sorts the DataFrame by index

D Does nothing

reset_index() moves the current index into columns and resets the index to default integers starting at 0.

How do you reset the index without keeping the old index as a column?

A reset_index(keep_index=True)

B reset_index(drop=True)

C reset_index(drop=False)

D reset_index(remove=True)

Using drop=True removes the old index instead of adding it as a column.

After filtering rows, why might you want to reset the index?

A To get a clean, sequential index starting at 0

B To delete the DataFrame

C To sort the rows alphabetically

D To add new columns

Filtering can leave gaps in the index; resetting fixes this by creating a new sequential index.

What does reset_index() do with a MultiIndex DataFrame?

A Converts MultiIndex to a single index

B Deletes the DataFrame

C Leaves the MultiIndex unchanged

D Moves all index levels to columns and resets index

It moves all levels of the MultiIndex into columns and resets the index to default integers.

Which of these is NOT a reason to reset a DataFrame index?

A To prepare data for export

B To fix gaps after filtering

C To permanently delete data

D To simplify the index

Resetting index does not delete data; it only changes the index structure.

Explain what happens when you use reset_index() on a pandas DataFrame.

Think about how the index changes and what happens to the old index.

Describe a situation where resetting the index of a DataFrame is useful.

Consider what happens to the index after removing some rows.