Adding element to list in pandas column

Question

I can't figure out how to add element to pandas column for single row.

index = ['a','b','c','d']
df = pd.DataFrame(index = index)
df['Col'] = [[]] * len(index)

df.loc['d','Col'].append('AA')

returns:

    Col
a   [AA]
b   [AA]
c   [AA]
d   [AA]

I look for value 'AA' to be in the last row only.

score 2 · Accepted Answer · answered Feb 17 '20 at 21:21

2

We should create the list of empty list by , avoid same object assignment. Also you can use .loc for assign the value in pandas

df['Col'] = [[] for x in df.index]
df.loc['d','Col']='AA'
df
  Col
a  []
b  []
c  []
d  AA

df.loc['d','Col'].append('AA')
df
    Col
a    []
b    []
c    []
d  [AA]

answered Feb 17 '20 at 21:21

BENY

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Thank you. I will read the explanation in linked post. – Ranny Feb 17 '20 at 21:32

Thales Marques · Answer 2 · 2020-02-17T21:24:15.277

0

Try

df.loc['d','Col'] = 'AA'

This should work for you

Edit:

Based on your edit, maybe this could be more efficient:

df.iloc[-1] = [['AA']]

edited Feb 17 '20 at 21:24

answered Feb 17 '20 at 21:18

Thales Marques

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you are not adding a value to the list... – luigigi Feb 17 '20 at 21:18
I'm sorry, but the title of the question is confused and seems to be different of what Ranny is asking. I believe that Ranny is trying to insert a value in a specific position of the data frame. Is that correct? – Thales Marques Feb 17 '20 at 21:20
yea, maybe – luigigi Feb 17 '20 at 21:21
it works, but I iterate and add elements to list in each row one by one. This method will do but it seems to me a long way around some simpler solution. – Ranny Feb 17 '20 at 21:21
check my edit and let me know if it works for you – Thales Marques Feb 17 '20 at 21:25

Adding element to list in pandas column

2 Answers2