Calculating Length of List of List in Pandas

Question

I have a problem that is extension to this and this. Suppose I have dataframe like this:

    A   B
0   1   [["Thing_1"]]
1   2   [["Thing_1"], ["Thing_2"]]
2   3   [["Thing_1", "Thing_2"], ["Thing_2"]]
3   4   [["Thing_1"], ["Thing_1", "Thing_2"]]
4   5   [["Thing_1", "Thing_2"], ["Thing_1", "Thing_2"]]

Instead of getting like this:

    A   B                                                 C(result of length in column B)
0   1   [["Thing_1"]]                                     1
1   2   [["Thing_1"], ["Thing_2"]]                        2
2   3   [["Thing_1", "Thing_2"], ["Thing_2"]]             2
3   4   [["Thing_1"], ["Thing_1", "Thing_2"]]             2
4   5   [["Thing_1", "Thing_2"], ["Thing_1", "Thing_2"]]  2

the column C becomes the length of the characters in the lists of lists rather than the outer length of lists of lists using these functions: df['B'].str.len() and df['B'].apply(len). How can I get the result right?

`df.B.str.len()` seems to work fine – sammywemmy Aug 19 '20 at 07:41 — sammywemmy, Aug 19 '20 at 07:41

MrNobody33 · Accepted Answer · 2020-08-19T07:52:28.227

I think maybe your column B is actually of type string, since it's giving you a length of the characters, so try first with ast.literal_eval to change the column from string type to lists, and then use df['B'].apply(len) or df['B'].str.len()

import ast
df['B']=df['B'].apply(ast.literal_eval)
df['C']=df['B'].apply(len)

Or if you only need the length without changing the type of column B, try with a single apply

df['C']=df['B'].apply(lambda x:ast.literal_eval(x)).str.len()

Output:

df
   A                                                 B  C
0  1                                     [["Thing_1"]]  1
1  2                        [["Thing_1"], ["Thing_2"]]  2
2  3             [["Thing_1", "Thing_2"], ["Thing_2"]]  2
3  4             [["Thing_1"], ["Thing_1", "Thing_2"]]  2
4  5  [["Thing_1", "Thing_2"], ["Thing_1", "Thing_2"]]  2

Thanks! Actually, I had figured that about three minutes before you answered, but nevertheless, since you pointed out my problem, you'd have my vote. — lolikianoaholting, Aug 19 '20 at 12:53
You´re welcome, no worries, glad you found a solution to your problem! Happy coding!:) — MrNobody33, Aug 19 '20 at 14:33

Calculating Length of List of List in Pandas

1 Answers1