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pythonpandasdataframefill

fill a dataframe with value of another dataframe according to columns value

I have two dataframe:

the first one, let's say dfrA

x,y,z
0,0,1
0,1,2
0,2,3
0,3,4
1,0,5
1,1,6
1,2,7
1,3,8
2,0,9
2,1,10
2,2,11
2,3,12
3,0,13
3,1,14
3,2,15
3,3,16

and another one, let's say dfrB

x,y
1,2
2,3

I would like to add a column in dfrB according with z value in the dfrA which has the same x and y of the dfrB.

In other words I expect:

x,y,z
1,2,7
2,3,12

I am able to a empty column to dfrB:

df_support = pd.DataFrame(columns=['z'])
dfrB = dfrB.join(df_support, how="outer")

how can now fill column z in dfrB? I would like to avoid to do a cycle full of if.

Solution

  • You can try pandas.DataFrame.merge

    dfrB['z'] = dfrB.merge(dfrA, on=['x', 'y'], how='left')['z']

    print(dfrB)

   x  y   z
0  1  2   7
1  2  3  12