create pandas column with new values based on values in other columns

Question

dataframe a:

    id    value
-------------------------------
0   231   9243
1   392   81139
2   493   896546
3   879   31

dataframe b:

   id   description  colour
-------------------------------
0  231  football     brown
1  392  bat          white
2  556  chicken      yellow 
3  493  tennis ball  yellow
4  119  pig          pink
5  879  cricket ball red

My question is how can I create a new column in dataframe a that inputs the description from dataframe b based on matching to the id column values in dataframe a? So I end up with:

    id    description    value    
-------------------------------
0   231   football        9243
1   392   bat             81139
2   493   tennis ball     896546
3   879   cricket ball    31

SeaBean · Accepted Answer · 2021-05-06 09:07:54Z

1

You can create a dict for mapping id and description from dataframe b and then use .map() on dataframe a on id columns, as follows:

b_dict = dict(zip(b['id'], b['description']))
a['description'] = a['id'].map(b_dict).fillna('')

Result:

print(a)

    id   value   description
0  231    9243      football
1  392   81139           bat
2  493  896546   tennis ball
3  879      31  cricket ball

answered May 6, 2021 at 9:07

SeaBean

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Nk03 · Accepted Answer · 2021-05-06 09:04:20Z

1

via left merge

df1 = df1.merge(df2[['id','description']], on='id', how='left')

output

    id   value   description
0  231    9243      football
1  392   81139           bat
2  493  896546   tennis_ball
3  879      31  cricket_ball

answered May 6, 2021 at 9:04

Nk03

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