How to drop element from a list inside a pandas column in Python?

Question

I have a column in a dataframe that contain a list inside. My dataframe column is:

 [],
 ['NORM'],
 ['NORM'],
 ['NORM'],
 ['NORM'],
 ['MI', 'STTC'],

As you can see I have an empty list and also a list with two elements. How can I change list with two elements to just take one of it (I don't care which one of it). I tried with df.column.explode()but this just add more rows and I don't want more rows, I just need to take one of it. Thank you so much

Shubham Sharma · Accepted Answer · 2020-07-02 15:17:45Z

1

You can use Series.map with a custom mapping function which maps the elements of column according to desired requirements:

df['col'] = df['col'].map(lambda l: l[:1])

Result:

# print(df['col'])

0        []
1    [NORM]
2    [NORM]
3    [NORM]
4    [NORM]
5      [MI]

edited Jul 2, 2020 at 15:17

answered Jul 2, 2020 at 15:11

Shubham Sharma

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Comments

Sai · Accepted Answer · 2020-07-02 15:08:23Z

1

i, j is the location of the cell you need to access and this will give the first element of the list

list_ = df.loc[i][j]
if len(list_) > 0:
   print(list_[0])

answered Jul 2, 2020 at 15:08

Sai

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Comments

Serge Ballesta · Accepted Answer · 2020-07-02 15:14:04Z

1

As you store lists into a pandas column, I assume that you do not worry for vectorization. So you could just use a list comprehension:

df[col] = [i[:1] for i in df[col]]

answered Jul 2, 2020 at 15:14

Serge Ballesta

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