Counting how many times a value appears in polars

value_counts

When dealing with categorical data, you may want to know how many times each category appears in a column. Below is a dataframe containing three different categories of clothing items.

shape: (1_000, 2)

category	quantity
str	i64
"Hat"	1
"Sweater"	9
"Sweater"	12
"Sweater"	5
"Sweater"	19
…	…
"Sweater"	2
"Socks"	19
"Socks"	18
"Sweater"	15
"Sweater"	11

Count appearance of values

To count how many times each clothing category appears in the dataframe above, you can use value_counts in Polars. Here’s how to do it:

(df
 ['category']
 .value_counts(sort=True)
 )

shape: (3, 2)

category	count
str	u32
"Sweater"	526
"Socks"	297
"Hat"	177

Doing it the idiomatic way

If you want to impress your colleagues with your Polars knowledge, you can do it the idiomatic way (which I highly encourage).

(df
 .select('category')
 .to_series()
 .value_counts(sort=True)
 )

shape: (3, 2)

category	count
str	u32
"Sweater"	526
"Socks"	297
"Hat"	177

For more idiomatic ways, enroll in my Polars course