merge two files based on common column values

Question

I have file1 likes:

1 A aa
2 A bb
3 A cc
4 A dd
5 B xx
6 C yy
7 C zz

And a file2:

1 A 11
2 B 22
3 C 33

And I

Answer 1

Using pandas will save you a lot of time if you use Python. So if your DataFrames are df1:

   1   2
0
1  A  aa
2  A  bb
3  A  cc
4  A  dd
5  B  xx
6  C  yy
7  C  zz

and df2:

   1   2
0
1  A  11
2  B  22
3  C  33

then you can use merge:

df1.merge(df2, left_on=1, right_on=1)

to get

   1 2_x  2_y
0  A  aa   11
1  A  bb   11
2  A  cc   11
3  A  dd   11
4  B  xx   22
5  C  yy   33
6  C  zz   33

Answer 2

Which way is the simplest

I am not sure what do you mean by simplest. For this problem, you can simply use join:

join -j 2 -o 1.1 1.2 1.3 2.3 file1 file2

For the given example, the above command generates the desired output. If your file is not sorted, you can also add --nocheck-order option.