Python Pandas merge only certain columns

Question

Is it possible to only merge some columns  I have a DataFrame df1 with columns x  y  z  and df2 with columns x  a  b  c  d  e  f  etc   I want to merge the two DataFrames on x  but I only want to merge columns df2 a  df2 b - not the entire DataFrame    The result would be a DataFrame with x  y  z  a  b   I could merge then delete the unwanted columns  but it seems like there is a better method

User · Answer

You can use  loc to select the specific columns with all rows and then pull that  An example is below   pandas merge dataframe1  dataframe2 iloc     0 5    how  left   on  key     In this example  you are merging dataframe1 and dataframe2  You have chosen to do an outer left join on  key   However  for dataframe2 you have specified  iloc which allows you to specific the rows and columns you want in a numerical format  Using    your selecting all rows  but  0 5  selects the first 5 columns  You could use  loc to specify by name  but if your dealing with long column names  then  iloc may be better

User · Answer

You could merge the sub-DataFrame  with just those columns    df2 list  xab       df2 but only with columns x  a  and b  df1 merge df2 list  xab

User · Answer

If you want to drop column s  from the target data frame  but the column s  are required for the join  you can do the following   df1   df1 merge df2   a    b    key1     how    left                   left on    key2   right on    key1   drop  key1     The  drop  key1   part will prevent  key1  from being kept in the resulting data frame  despite it being required to join in the first place

User · Answer

This is to merge selected columns from two tables   If table 1 contains t1 a t1 b t1 c   id   t1 z columns  and table 2 contains t2 a  t2 b  t2 c     id   t2 z columns  and only t1 a  id  t2 a are required in the final table  then  mergedCSV   table 1   t1 a   id    merge table 2   t2 a   id     on    id  how    left     save resulting output file     mergedCSV to csv  output csv  index   False

User · Answer

You want to use TWO brackets  so if you are doing a VLOOKUP sort of action   df   pd merge df df2   Key Column   Target Column    on  Key Column   how  left     This will give you everything in the original df   add that one corresponding column in df2 that you want to join

[python] Python Pandas merge only certain columns

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