how to set values to rows of boolean filtered dataframe column

Question

I'm trying to set the values of "FreeSec" column to True for the filtered rows of my pandas dataframe. Here is the code:

data[data["Brand"].isin(group_clients)].FreeSec = True

However, when I check the values they are still set to False.

>>> data[data["Brand"].isin(group_clients)].FreeSec

12     False
163    False
164    False
165    False
166    False
167    False
168    False
169    False

What am I missing here?

Answer 1

You should use loc to do this without chaining, which will garauntee that assignment works:

data.loc[data["Brand"].isin(group_clients), "FreeSec"] = True

Assignment in loc is overridden so that the implementation detail of whether it's actually a view or a copy doesn't matter, it does matter if you chain so avoid/be very careful.