Python Pandas: Stack a column in a DataFrame

pandas_stack_column.py

import pandas as pd


def stack_with_column(df, column, sep=','):
    """Stack a column splitting with `sep` in a DataFrame.
    """
    stacked_column = (
        df[column].str.split(sep, expand=True)
        .stack()
        .reset_index(1, drop=True)
        .to_frame(column)
    )
    original_without_column = df.drop(column, axis=1)
    stacked = (
        original_without_column
        .join(stacked_column)
        .reset_index(drop=True)
        [df.columns]
    )
    return stacked


df = pd.DataFrame({
    'other1': ['a', 'b'],
    'other2': ['c', 'd'],
    'gene': ['GSTM1', 'LOC101927027,PRKRA'],
})
# =>
#   other1 other2                gene
# 0      a      d               GSTM1
# 1      b      e  LOC101927027,PRKRA


stack_with_column(df)
# =>
#   other1 other2          gene
# 0      a      c         GSTM1
# 1      b      d  LOC101927027
# 2      b      d         PRKRA