I have two columns with list in in. How do I combine these two list into a new column element for el-CodePudding

So I have for example a DataFrame with the two columns:

col1               col2
['1', '2', '3']    ['A', 'B', 'C']
['4', '5', '6']    ['D', 'E', 'F']
etc.

I would like to get a third column with:

col3
[['1', 'A'], ['2', 'C'], ['3', 'C']]
[['4', 'D'], ['5', 'E'], ['6', 'F']] 
etc

I have tried to use apply and combine it with a lambda function like this:

df['col3'] = df.apply(lambda x: [y,z] for y,z in zip(x['col1'], x['col2']), axis=1)

But this only give the error:

SyntaxError: Generator expression must be parenthesized

Can some help me?

CodePudding user response：

In your solution add [] for list comprehension:

df['col3'] = df.apply(lambda x: [[y,z] for y,z in zip(x['col1'], x['col2'])], axis=1)
print (df)
        col1       col2                      col3
0  [1, 2, 3]  [A, B, C]  [[1, A], [2, B], [3, C]]
1  [4, 5, 6]  [D, E, F]  [[4, D], [5, E], [6, F]]

Or use nested list comprehension:

df['col3'] = [[[a, b] for a, b in zip(*x)] for x in zip(df['col1'], df['col2'])]
print (df)
        col1       col2                      col3
0  [1, 2, 3]  [A, B, C]  [[1, A], [2, B], [3, C]]
1  [4, 5, 6]  [D, E, F]  [[4, D], [5, E], [6, F]]

CodePudding user response：

IIUC you could use list(map(list,zip(*r))) and result_type='reduce' in apply:

df['col3'] = df.apply(lambda r: list(map(list,zip(*r))),
                      result_type='reduce', axis=1)

output:

        col1       col2                      col3
0  [1, 2, 3]  [A, B, C]  [[1, A], [2, B], [3, C]]
1  [4, 5, 6]  [D, E, F]  [[4, D], [5, E], [6, F]]

If you want to limit the processing to a subset of columns:

cols = ['col1', 'col2']
df['col3'] = df[cols].apply(lambda r: list(map(list,zip(*r))),
                            result_type='reduce', axis=1)