How to create new columns depending on row value in pandas

Question

I have a dataframe that looks like this:

    time  speaker  label_1  label_2
0   0.25        1       10        4
1   0.25        2       10        5
2   0.50             


        

Answer 1

First we use pivot_table to pivot our rows to columns. Then we create our desired column names by string concatenating with list_comprehension and f-string:

piv = df.pivot_table(index='time', columns='speaker')
piv.columns = [f'spk_{col[1]}_{col[0]}' for col in piv.columns]

      spk_1_label_1  spk_2_label_1  spk_1_label_2  spk_2_label_2
time                                                            
0.25             10             10              4              5
0.50             10             10              6              7
0.75             10             10              8              9
1.00             10             10             11             12
1.25             11             11             13             14
1.50             11             11             15             16
1.75             11             11             17             18
2.00             11             11             19             20

If you want to remove the index name:

piv.rename_axis(None, inplace=True)

      spk_1_label_1  spk_2_label_1  spk_1_label_2  spk_2_label_2
0.25             10             10              4              5
0.50             10             10              6              7
0.75             10             10              8              9
1.00             10             10             11             12
1.25             11             11             13             14
1.50             11             11             15             16
1.75             11             11             17             18
2.00             11             11             19             20

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Extra

If you want, we can make it more general by using the column name as prefix for your flattened columns:

piv.columns = [f'{piv.columns.names[1]}_{col[1]}_{col[0]}' for col in piv.columns]

      speaker_1_label_1  speaker_2_label_1  speaker_1_label_2  speaker_2_label_2
time                                                                            
0.25                 10                 10                  4                  5
0.50                 10                 10                  6                  7
0.75                 10                 10                  8                  9
1.00                 10                 10                 11                 12
1.25                 11                 11                 13                 14
1.50                 11                 11                 15                 16
1.75                 11                 11                 17                 18
2.00                 11                 11                 19                 20

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Notice: if your python version < 3.5, you can't use f-strings, we can use .format for our string formatting:

['spk_{}_{}'.format(col[0], col[1]) for col in piv.columns]