How to convert list column to a non-nested list?

Question

How to convert a column to a non-nested list while the column elements are list?

For example, the column is like

column
[1, 2, 3]
[1, 2]

<

Answer 1

You can use numpy.concatenate:

print (np.concatenate(df['column'].values).tolist())
[1, 2, 3, 1, 2]

Or:

from  itertools import chain
print (list(chain.from_iterable(df['column'])))
[1, 2, 3, 1, 2]

Another solution, thanks juanpa.arrivillaga:

print ([item for sublist in df['column'] for item in sublist])
[1, 2, 3, 1, 2]

Timings:

df = pd.DataFrame({'column':[[1,2,3], [1,2]]})
df = pd.concat([df]*10000).reset_index(drop=True)
print (df)

In [77]: %timeit (np.concatenate(df['column'].values).tolist())
10 loops, best of 3: 22.7 ms per loop

In [78]: %timeit (list(chain.from_iterable(df['column'])))
1000 loops, best of 3: 1.44 ms per loop

In [79]: %timeit ([item for sublist in df['column'] for item in sublist])
100 loops, best of 3: 2.31 ms per loop

In [80]: %timeit df.column.sum()
1 loop, best of 3: 1.34 s per loop