Pandas column of lists, create a row for each list element

Question

I have a dataframe where some cells contain lists of multiple values. Rather than storing multiple values in a cell, I\'d like to expand the dataframe so that each item in t

Answer 1

Also very late, but here is an answer from Karvy1 that worked well for me if you don't have pandas >=0.25 version: https://stackoverflow.com/a/52511166/10740287

For the example above you may write:

data = [(row.subject, row.trial_num, sample) for row in df.itertuples() for sample in row.samples]
data = pd.DataFrame(data, columns=['subject', 'trial_num', 'samples'])

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Speed test:

%timeit data = pd.DataFrame([(row.subject, row.trial_num, sample) for row in df.itertuples() for sample in row.samples], columns=['subject', 'trial_num', 'samples'])

1.33 ms ± 74.8 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)

%timeit data = df.set_index(['subject', 'trial_num'])['samples'].apply(pd.Series).stack().reset_index()

4.9 ms ± 189 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)

%timeit data = pd.DataFrame({col:np.repeat(df[col].values, df['samples'].str.len())for col in df.columns.drop('samples')}).assign(**{'samples':np.concatenate(df['samples'].values)})

1.38 ms ± 25 µs per loop (mean ± std. dev. of 7 runs, 1000 loops each)