isin() for value matching in Pandas - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the isin() function do in pandas?

The isin() function checks if each element in a pandas Series or DataFrame is contained in a list or set of values. It returns a boolean Series or DataFrame showing True where the element matches any value in the list, and False otherwise.

beginner

How do you use isin() to filter rows in a DataFrame?

You use isin() on a DataFrame column to get a boolean Series, then use that Series to select rows. For example, df[df['column'].isin([value1, value2])] returns rows where the column's value is either value1 or value2.

intermediate

Can isin() be used with multiple columns in a DataFrame?

Yes, you can apply isin() to multiple columns separately or use it on the entire DataFrame to check if each element is in a list of values. It returns a DataFrame of booleans with the same shape as the original.

beginner

What type of object does isin() return when used on a Series?

isin() returns a pandas Series of boolean values. Each boolean indicates whether the corresponding element in the original Series is in the list of values provided.

beginner

Why is isin() useful in data analysis?

isin() helps quickly find and filter data points that match a set of values. This is useful for selecting specific categories, cleaning data, or comparing data against a list of known values.

What does df['A'].isin([1, 2, 3]) return?

A A DataFrame filtered to only rows where 'A' is 1, 2, or 3

B A list of values 1, 2, and 3

C A boolean Series showing True where values in column 'A' are 1, 2, or 3

D An error because <code>isin()</code> cannot take a list

isin() returns a boolean Series indicating which values in the column match any value in the list.

How can you use isin() to select rows where column 'color' is either 'red' or 'blue'?

A df[df['color'].isin(['red', 'blue'])]

B df.isin(['red', 'blue'])

C df['color'] == ['red', 'blue']

D df['color'].contains(['red', 'blue'])

Using isin() on the 'color' column with the list ['red', 'blue'] returns a boolean Series to filter rows.

What type of object can you pass as an argument to isin()?

A Only a DataFrame

B Only a single value

C Only a dictionary

D List, set, or Series of values

isin() accepts any iterable like list, set, or Series to check membership.

If you use df.isin([1, 2]) on a DataFrame, what is the output?

A A DataFrame of booleans showing True where elements are 1 or 2

B A filtered DataFrame with only rows containing 1 or 2

C A Series of booleans for the first column

D An error because <code>isin()</code> only works on Series

When used on a DataFrame, isin() returns a DataFrame of the same shape with True/False values.

Which of these is NOT a correct use of isin()?

A df.isin({10, 20})

B df['col'].isin(10)

C df['col'].isin([10, 20])

D df.isin(pd.Series([10, 20]))

Passing a single value like 10 directly is invalid; isin() expects an iterable like list or set.

Explain how you would use isin() to filter a DataFrame for rows where a column matches any value from a list.

Think about how to get True/False for each row and then select rows.

Describe the difference in output when using isin() on a pandas Series versus on a DataFrame.

Consider the shape and type of the output.