Conditionally concat a dataframe in python using pandas -


i have data frame

df 

     b 0  test1  1 1  test2  4 2  test3  1 3  test4  2

df1

   c 0  test3 1  test5

i want conditionally merge them new dataframe

df2

     b 0  test1   1 1  test2   4 2  test3   0 3  test4   2 4  test5   0

a new data frame if value in column equal column c, while merging update column b value default of 0 , if there there isn't value exists in column equal value in column c add data frame shown above default value of 0.

here simple approach. take element second dataframe in col c not in col a on first dataframe - , concatenate setting missing values 0. use small hack in groupby in case there several same values in col a, select 1 0:

pd.concat([df,df1.rename(columns={'c':'a'})]).fillna(0).groupby('a', as_index=false).last()          b 0  test1  1 1  test2  4 2  test3  0 3  test4  2 4  test5  0

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