Get indices for a specific value in a polars dataframe

arg_true

100DaysOfPolars
Author

Joram Mutenge

Published

2025-10-26

Sometimes you may want to get the index positions of a repeating value in a Polars dataframe. Below is a dataframe showing students and their grades.

shape: (20, 2)
Student Grade
str i64
"Spencer" 93
"Spencer" 88
"Emily" 73
"Emily" 69
"Hannah" 55
"Hannah" 89
"Aria" 92
"Aria" 81
"Mona" 97
"Paige" 71


Get index of rows

To get the index positions of rows where the name “Aria” appears, use the Polars expression arg_true like this:

(df
 .select((pl.col('Student') == 'Aria').arg_true())
 )
shape: (4, 1)
Student
u32
6
7
16
17


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