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How can the dataframe for Polars be modified to ensure that each id variable has an equal number of rows?

asked 2021-09-03 11:00:00 +0000

plato gravatar image

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answered 2022-06-20 15:00:00 +0000

devzero gravatar image

To modify the dataframe for Polars to ensure that each id variable has an equal number of rows, you can use the groupby() function to group the DataFrame by the id variable, and then use the sample() function to sample a fixed number of rows from each group. Here is an example code snippet:

import polars as pl

# create example DataFrame
df = pl.DataFrame({
    "id": [1, 1, 1, 2, 2, 3, 3],
    "value": [10, 20, 30, 40, 50, 60, 70]

# determine number of rows per id
n_rows_per_id = df.groupby("id").count().max()["value"]

# sample fixed number of rows from each id group
df = df.groupby("id").sample(n_rows_per_id)

In this example, n_rows_per_id is determined by grouping the DataFrame by the id variable and counting the number of rows in each group using count(), and then taking the maximum value of the value column (which is the count for the largest group).

Then, the sample() function is used to sample n_rows_per_id rows from each group of the DataFrame, resulting in a new DataFrame where each id variable has the same number of rows.

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Asked: 2021-09-03 11:00:00 +0000

Seen: 6 times

Last updated: Jun 20 '22