Warning when adding a column to a dataframe with the same value

Asked Dec 12 '22 at 14:06

Active Dec 12 '22 at 14:06

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How can I add a column to a dataframe with the same value

I've tried

dataframe['size']=10

dataframe.loc[:,'size']=10

but this gives

A value is trying to be set on a copy of a slice from a DataFrame.
Try using .loc[row_indexer,col_indexer] = value instead

See the caveats in the documentation: https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#returning-a-view-versus-a-copy

asked Dec 12 '22 at 14:06

KansaiRobot

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Does this answer your question? [Add column to dataframe with constant value](https://stackoverflow.com/questions/29517072/add-column-to-dataframe-with-constant-value) – Azhar Khan Dec 12 '22 at 14:07
You are doing it right with `dataframe['size']=10`. – Azhar Khan Dec 12 '22 at 14:08
@AzharKhan Then why the warning? – KansaiRobot Dec 12 '22 at 14:09
Is `dataframe` a ref to full dataframe or view (sub-dataframe)? – Azhar Khan Dec 12 '22 at 14:09
it is `dataframe=df[df['other']==something]` – KansaiRobot Dec 12 '22 at 14:10
`dataframe.loc[:,'size']` returns a view of dataframe. So warning there is explained at https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html#returning-a-view-versus-a-copy. – Azhar Khan Dec 12 '22 at 14:11
the warning also appear on `dataframe['size']=10` – KansaiRobot Dec 12 '22 at 14:11
I explained it [here](https://stackoverflow.com/a/74487768/2847330). Your `dataframe` is a view of some dataframe. – Azhar Khan Dec 12 '22 at 14:14

Warning when adding a column to a dataframe with the same value

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