Detecting missing values with isna() in Pandas - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the isna() function do in pandas?

The isna() function checks each value in a pandas DataFrame or Series and returns True if the value is missing (NaN), otherwise False.

beginner

How can you use isna() to find missing values in a DataFrame?

Call isna() on the DataFrame. It returns a DataFrame of the same shape with True where values are missing and False elsewhere.

beginner

What type of output does isna() produce when used on a pandas Series?

It produces a Series of boolean values, where each element is True if the original value is missing, and False if it is present.

intermediate

Can isna() detect missing values represented as None in pandas?

Yes, isna() treats both None and NaN as missing values and returns True for them.

beginner

How is isna() different from notna() in pandas?

isna() returns True for missing values, while notna() returns True for non-missing values.

What does df.isna() return when called on a pandas DataFrame df?

A A DataFrame of booleans showing where values are missing

B A count of missing values in each column

C A DataFrame with missing values replaced by zeros

D A list of column names with missing values

isna() returns a DataFrame of the same shape with True where values are missing and False elsewhere.

Which of these values will isna() mark as missing in pandas?

A None

B "" (empty string)

C 0

D False

isna() treats None and NaN as missing values. Zero, empty string, and False are not missing.

If series is a pandas Series, what is the type of series.isna()?

A DataFrame of booleans

B Series of booleans

C List of missing values

D Integer count of missing values

isna() on a Series returns a Series of booleans indicating missing values.

Which pandas function gives the opposite result of isna()?

A fillna()

B dropna()

C isnull()

D notna()

notna() returns True for non-missing values, opposite of isna().

What will df.isna().sum() do?

A Replace missing values with sum

B Return total number of rows

C Count missing values in each column

D Drop rows with missing values

isna() marks missing values, and sum() counts True values per column, giving missing value counts.

Explain how you would use pandas to find missing values in a dataset.

Think about a function that marks missing spots with True.

Describe the difference between isna() and notna() in pandas.

One finds missing, the other finds present values.