Append column to pandas dataframe

Question

This is probably easy  but I have the following data   In data frame 1   index dat1 0     9 1     5   In data frame 2   index dat2 0     7 1     6   I want a data frame with the following form   index dat1  dat2 0     9     7 1     5     6   I ve tried using the append method  but I get a cross join  i e  cartesian product    What s the right way to do this

User · Accepted Answer

It seems in general you re just looking for a join    gt  dat1   pd DataFrame   dat1    9 5     gt  dat2   pd DataFrame   dat2    7 6     gt  dat1 join dat2     dat1  dat2 0     9     7 1     5     6

User · Answer

Both join   and concat   way could solve the problem  However  there is one warning I have to mention  Reset the index before you join   or concat   if you trying to deal with some data frame by selecting some rows from another DataFrame    One example below shows some interesting behavior of join and concat   dat1   pd DataFrame   dat1   range 4    dat2   pd DataFrame   dat2   range 4 8    dat1 index    1 3 5 7  dat2 index    2 4 6 8     way1 join 2 DataFrames print dat1 join dat2     output    dat1  dat2 1     0   NaN 3     1   NaN 5     2   NaN 7     3   NaN    way2 concat 2 DataFrames print pd concat  dat1 dat2  axis 1    output    dat1  dat2 1   0 0   NaN 2   NaN   4 0 3   1 0   NaN 4   NaN   5 0 5   2 0   NaN 6   NaN   6 0 7   3 0   NaN 8   NaN   7 0   reset index  dat1   dat1 reset index drop True  dat2   dat2 reset index drop True   both 2 ways to get the same result  print dat1 join dat2      dat1  dat2 0     0     4 1     1     5 2     2     6 3     3     7   print pd concat  dat1 dat2  axis 1      dat1  dat2 0     0     4 1     1     5 2     2     6 3     3     7

User · Answer

Just a matter of the right google search   data   dat 1 append dat 2  data   data groupby data index  sum

User · Answer

You can also use   dat1   pd concat  dat1  dat2   axis 1

User · Answer

Just as a matter of fact   data joined   dat1 join dat2  print data joined

[python] Append column to pandas dataframe

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