'Pandas: How To Convert From 'Frequency Table' To Flat Dataframe Format? [duplicate]

How do I convert a Pandas dataframe from a 'frequency table' format to a flat dataframe format and back again using idiomatic Python?

From:

        H     E     K
0       B     B    12
1       B     G     3
2       G     B    17
3       G     G    68

to:

        H     E
0       B     B
1       B     B
2       B     B
3       B     B
4       B     B
5       B     B
6       B     B
7       B     B
8       B     B
9       B     B
10      B     B
11      B     B
12      B     G
13      B     G
14      B     G
...

and back again!

        H     E     K
0       B     B    12
1       B     G     3
2       G     B    17
3       G     G    68

Please advise?

pandasfrequency-table


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