Append a string item to lists in a Pandas Column

Question

For a pandas dataframe:

Name:        Tags:
'One'        ['tag1', 'tag3']
'Two'        []
'Three'      ['tag1']

How can 'tag2' be appended to the tags lists?

I have tried the following (addtag2 is another df):

df['Tags'] = df['Tags'].astype(str) + ', ' + addtag2['Tags'].astype(str)

and

df['Tags'] = df['Tags'].add(addtag2['Tags'].astype(str))

But they append the string outside the list eg ['tag1'], tag2 or ['tag1']tag2

The desired output would be:

Name:        Tags:
'One'        ['tag1', 'tag3', 'tag2']
'Two'        ['tag2']
'Three'      ['tag1', 'tag2']

Quang Hoang · Accepted Answer · 2020-06-02 17:00:32Z

2

This is an instance where apply comes handy:

df['Tags'] = df['Tags'].apply(lambda x: x + ['tag2'])

Or you can do a for loop:

for x in df.Tags: x.append('tag2')

Output:

    Name                Tags
0    One  [tag1, tag3, tag2]
1    Two              [tag2]
2  Three        [tag1, tag2]

answered Jun 2, 2020 at 17:00

Quang Hoang

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3 Comments

Tom Over a year ago

or df['Tags'].apply(lambda x: x.append('tag2'))

Tom Over a year ago

@QuangHoang it works for me; what do you mean? df['Tags'] = df['Tags'].apply(lambda x: x.append('tag2')) doesn't work, but if you just call the bit after the equals sign it works (the df is modified in place)

Quang Hoang Over a year ago

@Tom That's true. My apology.

Mayank Porwal · Accepted Answer · 2020-06-02 17:10:24Z

1

Or you can do this using append:

df['Tags'] = df['Tags'].apply(lambda x: x.append('tag2') or x)

Output:

    Name                Tags
0    One  [tag1, tag3, tag2]
1    Two              [tag2]
2  three        [tag1, tag2]

answered Jun 2, 2020 at 17:10

Mayank Porwal

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