CODEWITHSUNDEEP
python-3.xpandasdataframe
Ank
Ank

Reputation: 1904

Pandas add column using a list

I have a pandas dataframe like so:

col1 col2 col3
 1    8    6
 2    9    5
 5    3    9

Now I want to add a new column with values from a list for each and every row of my dataframe. So if my list is like so:

lst = ["a", "b","c"]

then I want the final dataframe to be like:

col1 col2 col3 name
 1    8    6    a
 1    8    6    b
 1    8    6    c
 2    9    5    a
 2    9    5    b
 2    9    5    c
 5    3    9    a
 5    3    9    b
 5    3    9    c

Upvotes: 1

Views: 149

Answers (1)

jezrael
jezrael

Reputation: 863741

First idea is use Index.repeat by length of list and then append new column with numpy.tile:

lst = ["a", "b","c"]

df1 = (df.loc[df.index.repeat(len(lst))]
             .assign(name=np.tile(lst, len(df)))
             .reset_index(drop=True))
print (df1)
   col1  col2  col3 name
0     1     8     6    a
1     1     8     6    b
2     1     8     6    c
3     2     9     5    a
4     2     9     5    b
5     2     9     5    c
6     5     3     9    a
7     5     3     9    b
8     5     3     9    c

Or use cross join with DataFrame from list:

df1 = df.assign(a=1).merge(pd.DataFrame({'name':lst, 'a':1}), on='a').drop('a', axis=1)
print (df1)
   col1  col2  col3 name
0     1     8     6    a
1     1     8     6    b
2     1     8     6    c
3     2     9     5    a
4     2     9     5    b
5     2     9     5    c
6     5     3     9    a
7     5     3     9    b
8     5     3     9    c

Upvotes: 1

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