Find the name of the column in a Pandas DF which contains the longest list

Question

Given a Pandas DataFrame with lists stored in several of the columns, is there a simple way to find the column name which contains the longest list for each row?

For example, with this data:

                          positive                 negative          neutral
1   [marvel, moral, bold, destiny]                       []   [view, should]
2                      [beautiful]      [complicated, need]               []
3                      [celebrate]   [crippling, addiction]            [big]

I want to identify "positive" as the column with the longest list for row 1 and "negative" for rows 2 and 3.

I thought I could use str.len() to calculate the list lengths and idmax() to get the column names, but can't figure out how to combine them.

Answer 1

IIUC:

In [227]: df.applymap(len).idxmax(axis=1)
Out[227]:
0    positive
1    negative
2    negative
dtype: object

Answer 2

>>> df.apply(lambda row: row.apply(len).argmax(), axis=1)
0    positive
1    negative
2    negative
dtype: object