How to Retrieve the Initial Row of Each Group in a Pandas DataFrame?

Pandas Dataframe: Retrieve the Initial Row of Each Group

Question

Consider a dataset represented as a pandas DataFrame with columns 'id' and 'value'. The objective is to identify the first row for each distinct combination of 'id' and 'value'.

Solution

To obtain the first row of each group, utilize df.groupby('id').first(). This method retrieves the first non-null element for each 'id' group.

If you require the 'id' column in the resulting DataFrame, you can employ df.groupby('id').first().reset_index().

To acquire the first 'n' records within each group, utilize df.groupby('id').head(n).reset_index(drop=True).

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