Compare two Pandas Columns with Another DataFrame

Question

I have a master dataframe df1 which has unique column combinations ('a' and 'b')

df1:
a   b
A   1 
B   4 
K   5

I want to use these combinations to compare df2, iterating through each column and returning True or False based on whether the combination in df2 matches that of df1.

 df2:
a   b   c
A   1   TRUE
B   4   TRUE
K   1   FALSE

For example the 3rd row in df2 K, 1 does not match the K value in df1 (K,5). Just fyi, the number of rows will be larger for df2

Thanks a lot for your help.

jezrael · Accepted Answer · 2021-05-20 10:20:34Z

3

Use DataFrame.merge with indicator parameter and then compare by both value for boolean column:

df3 = df2.merge(df1, on=['a','b'], how='left',indicator='c')
df3['c'] = df3['c'].eq('both')

print (df3)
   a  b      c
0  A  1   True
1  B  4   True
2  K  1  False

answered May 20, 2021 at 10:20

jezrael

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