fillna not working together with column conditions in Pandas DataFrame











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I am trying to fill NaN values in a dataframe column, but only if a condition in another column is met (I'm working with Kaggle Titanic data). For example:




      Age    Title

0     10       Mr

1     2        Master

2     NaN      Master

3     NaN      Mr



In this table, I want to replace the NaN in the 'Age' column with a number, but only if the value in the 'Title' column is 'Master', not if it is 'Mr'. So I want to replace the row 2 NaN, not the row 3 NaN.



I'm trying this and don't understand why it doesn't work:



df.loc[df['Title'].str.contains('Master'),'Age'].fillna(some_number,inplace=True)


Can anyone help?






python dataframe null nan data-cleaning







share|improve this question


















  • 1




    what error do you get?
    – ehacinom
    Nov 21 at 21:49










  • Hi. Sorry, should have mentioned that. I don't get an error, it just does nothing and the NaN values do not get replaced.
    – Matthew Davies
    Nov 22 at 6:40










  • OK, so this works: df.loc[(df['Title'].str.contains('Master'))&(df['Age'].isnull()),'Age']=some_number. But I still don't get why my original code does not work.
    – Matthew Davies
    Nov 22 at 6:54

















up vote
1
down vote

favorite












I am trying to fill NaN values in a dataframe column, but only if a condition in another column is met (I'm working with Kaggle Titanic data). For example:




      Age    Title

0     10       Mr

1     2        Master

2     NaN      Master

3     NaN      Mr



In this table, I want to replace the NaN in the 'Age' column with a number, but only if the value in the 'Title' column is 'Master', not if it is 'Mr'. So I want to replace the row 2 NaN, not the row 3 NaN.



I'm trying this and don't understand why it doesn't work:



df.loc[df['Title'].str.contains('Master'),'Age'].fillna(some_number,inplace=True)


Can anyone help?






python dataframe null nan data-cleaning







share|improve this question


















  • 1




    what error do you get?
    – ehacinom
    Nov 21 at 21:49










  • Hi. Sorry, should have mentioned that. I don't get an error, it just does nothing and the NaN values do not get replaced.
    – Matthew Davies
    Nov 22 at 6:40










  • OK, so this works: df.loc[(df['Title'].str.contains('Master'))&(df['Age'].isnull()),'Age']=some_number. But I still don't get why my original code does not work.
    – Matthew Davies
    Nov 22 at 6:54















up vote
1
down vote

favorite









up vote
1
down vote

favorite











I am trying to fill NaN values in a dataframe column, but only if a condition in another column is met (I'm working with Kaggle Titanic data). For example:




      Age    Title

0     10       Mr

1     2        Master

2     NaN      Master

3     NaN      Mr



In this table, I want to replace the NaN in the 'Age' column with a number, but only if the value in the 'Title' column is 'Master', not if it is 'Mr'. So I want to replace the row 2 NaN, not the row 3 NaN.



I'm trying this and don't understand why it doesn't work:



df.loc[df['Title'].str.contains('Master'),'Age'].fillna(some_number,inplace=True)


Can anyone help?






python dataframe null nan data-cleaning







share|improve this question













I am trying to fill NaN values in a dataframe column, but only if a condition in another column is met (I'm working with Kaggle Titanic data). For example:




      Age    Title

0     10       Mr

1     2        Master

2     NaN      Master

3     NaN      Mr



In this table, I want to replace the NaN in the 'Age' column with a number, but only if the value in the 'Title' column is 'Master', not if it is 'Mr'. So I want to replace the row 2 NaN, not the row 3 NaN.



I'm trying this and don't understand why it doesn't work:



df.loc[df['Title'].str.contains('Master'),'Age'].fillna(some_number,inplace=True)


Can anyone help?






python dataframe null nan data-cleaning




python dataframe null nan data-cleaning






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked Nov 21 at 21:41









Matthew Davies

61




61








  • 1




    what error do you get?
    – ehacinom
    Nov 21 at 21:49










  • Hi. Sorry, should have mentioned that. I don't get an error, it just does nothing and the NaN values do not get replaced.
    – Matthew Davies
    Nov 22 at 6:40










  • OK, so this works: df.loc[(df['Title'].str.contains('Master'))&(df['Age'].isnull()),'Age']=some_number. But I still don't get why my original code does not work.
    – Matthew Davies
    Nov 22 at 6:54
















  • 1




    what error do you get?
    – ehacinom
    Nov 21 at 21:49










  • Hi. Sorry, should have mentioned that. I don't get an error, it just does nothing and the NaN values do not get replaced.
    – Matthew Davies
    Nov 22 at 6:40










  • OK, so this works: df.loc[(df['Title'].str.contains('Master'))&(df['Age'].isnull()),'Age']=some_number. But I still don't get why my original code does not work.
    – Matthew Davies
    Nov 22 at 6:54










1




1




what error do you get?
– ehacinom
Nov 21 at 21:49




what error do you get?
– ehacinom
Nov 21 at 21:49












Hi. Sorry, should have mentioned that. I don't get an error, it just does nothing and the NaN values do not get replaced.
– Matthew Davies
Nov 22 at 6:40




Hi. Sorry, should have mentioned that. I don't get an error, it just does nothing and the NaN values do not get replaced.
– Matthew Davies
Nov 22 at 6:40












OK, so this works: df.loc[(df['Title'].str.contains('Master'))&(df['Age'].isnull()),'Age']=some_number. But I still don't get why my original code does not work.
– Matthew Davies
Nov 22 at 6:54






OK, so this works: df.loc[(df['Title'].str.contains('Master'))&(df['Age'].isnull()),'Age']=some_number. But I still don't get why my original code does not work.
– Matthew Davies
Nov 22 at 6:54



















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