pandas merge join two data frames on multiple columns

Question

I am trying to join two pandas data frames using two columns   new df   pd merge A df  B df   how  left   left on   A c1 c2    right on     B c1 c2      but got the following error   pandas index pyx in pandas index IndexEngine get loc  pandas index c 4164     pandas index pyx in pandas index IndexEngine get loc  pandas index c 4028     pandas src hashtable class helper pxi in pandas hashtable PyObjectHashTable get item  pandas hashtable c 13166     pandas src hashtable class helper pxi in pandas hashtable PyObjectHashTable get item  pandas hashtable c 13120     KeyError    B 1  c2     Any idea what should be the right way to do this  Thanks

User · Accepted Answer

Try this new df   pd merge A df  B df   how  left   left on   A c1   c2    right on     B c1   c2     https   pandas pydata org pandas-docs stable reference api pandas DataFrame merge html  left on   label or list  or array-like Field names to join on in left DataFrame  Can be a vector or list of vectors of the length of the DataFrame to use a particular vector as the join key instead of columns right on   label or list  or array-like Field names to join on in right DataFrame or vector list of vectors per left on docs

User · Answer

Another way of doing this  new df   A df merge B df  left on   A c1   c2    right on     B c1   c2    how  left

User · Answer

the problem here is that by using the apostrophes you are setting the value being passed to be a string  when in fact  as  Shijo stated from the documentation  the function is expecting a label or list  but not a string  If the list contains each of the name of the columns beings passed for both the left and right dataframe  then each column-name must individually be within apostrophes  With what has been stated  we can understand why this is inccorect   new df   pd merge A df  B df   how  left   left on   A c1 c2    right on     B c1 c2      And this is the correct way of using the function   new df   pd merge A df  B df   how  left   left on   A c1   c2    right on     B c1   c2

[python] pandas: merge (join) two data frames on multiple columns

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