Get the index of unique values in a polars dataframe

arg_unique

You have a table with repeating names, and you want to get the index where each unique name appears. Below is a dataframe showing students and their grades on various tests.

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

Index where each unique value first appears

To get the index location where each unique name in the dataframe first appears, use the Polars expression arg_unique like this:

(df
 .select(pl.col('Student').arg_unique())
 )

shape: (6, 1)

Student
u32
0
2
4
6
8
9

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