Python reshaping according to column names and 1st column value

Question

I would like to reshape a data frame according to column names and first column's value. For example, I want to reshape this data frame:

hours mon tue wed
0     3   4   5
1     6   7   8
2     9   10  11

into following data frame:

hours day target
0     mon 3
1     mon 6
2     mon 9
0     tue 4
1     tue 7
2     tue 10
0     wed 5
1     wed 8
2     wed 11

Thanks in advance.

Answer 1

We can also use pd.lreshape:

In [118]: cols = df.columns.drop('hours').tolist()

In [119]: pd.lreshape(df, {'target':cols}).assign(day=np.repeat(cols, len(df)))
Out[119]:
   hours  target  day
0      0       3  mon
1      1       6  mon
2      2       9  mon
3      0       4  tue
4      1       7  tue
5      2      10  tue
6      0       5  wed
7      1       8  wed
8      2      11  wed

Answer 2

Use pandas.melt:

import pandas as pd
pd.melt(df, id_vars='hours', var_name='day', value_name='target')