How can I transform Tab 1 to Tab2

df = pd.DataFrame({'A': [3, 5], 'B': [4, 6], 'Z': [6, 8]}, index=[1, 100])

I suppose pandas df.melt might help, but I’m not sure

>Solution :

You can flatten your dataframe and manipulate index to get expected output:

out = (df.unstack().sort_index(level=1)
         .set_axis([f'{j}{i}' for i in df.index for j in df.columns])
         .rename_axis('var').rename('val').reset_index())

Output:

>>> out
    var  val
0    A1    3
1    B1    4
2    Z1    6
3  A100    5
4  B100    6
5  Z100    8