Pandas: Concat Data Frame With Different Column Name

Suppose I have this data frame id x y 0 a hello 0 b test 1 c hi 2 a hi 3 d bar I want to concat x and y into a single column like this keeping their i

Solution 1:

I don't think pandas.concat includes the option to set new column names (see docs), but you could assign like so:

Starting from:

   id  x      y
0   0  a  hello
1   0  b   test
2   1  c     hi
3   2  a     hi
4   3  d    bar

df.set_index('id', inplace=True)
pd.DataFrame(pd.concat([df.x, df.y]), columns=['xy']).reset_index()

   id     xy
0   0      a
1   0      b
2   1      c
3   2      a
4   3      d
5   0  hello
6   0   test
7   1     hi
8   2     hi
9   3    bar

Solution 2:

If ordering of rows is not important, you can use stack:

print df
   id  x      y
0   0  a  hello
1   0  b   test
2   1  c     hi
3   2  a     hi
4   3  d    bar

s = df.set_index('id').stack()
s.index = s.index.droplevel(-1)
s.name = 'xy'

print pd.DataFrame(s).reset_index()
   id     xy
0   0      a
1   0  hello
2   0      b
3   0   test
4   1      c
5   1     hi
6   2      a
7   2     hi
8   3      d
9   3    bar