Pandas Melt several groups of columns into multiple target columns by name

Question

I would like to melt several groups of columns of a dataframe into multiple target columns. Similar to questions Python Pandas Melt Groups of Initial Columns Into Multiple T

Answer 1

You can convert the column names to multi index based on the columns pattern and then stack at a particular level depending on the result you need:

import pandas as pd
df.set_index('id', inplace=True)
df.columns = pd.MultiIndex.from_tuples(tuple(df.columns.str.split("_")))
df.stack(level = 1).reset_index(level = 1, drop = True).reset_index()

# id    a   b    c      
#101    a   1   aa
#101    b   2   bb
#101    c   3   cc
#102    d   4   dd
#102    e   5   ee
#102    f   6   ff