Adding column to dataframe based on column's values

Question

I'm trying to add a column based on existing column values matching with a dataframe with a different length.

from pandas import DataFrame

    a = DataFrame([['a', '1'], ['b', 2], ['c', 3]], columns=['Letters', 'Numbers'])
    b = DataFrame([['a', '2001'], ['b', '2002'], ['c', '2003'], ['d', '2004']], columns=['Letters', 'Years'])

How can I add a column to a called Years which has the year where Letters of a and b match.

Desired output:

df = DataFrame([['a', '1', '2001'], ['b', 2, '2002'], ['c', 3, '2003']], columns=['Letters', 'Numbers', 'Years'])

jezrael · Accepted Answer · 2016-12-24 22:37:51Z

1

Use merge, if joined column is same in both DataFrame, parameter on can be omited, also by default is inner join, so parameter how is omit too:

print (pd.merge(a,b))
  Letters Numbers Years
0       a       1  2001
1       b       2  2002
2       c       3  2003

print (pd.merge(a,b, on='Letters'))
  Letters Numbers Years
0       a       1  2001
1       b       2  2002
2       c       3  2003

edited Dec 24, 2016 at 22:37

answered Dec 24, 2016 at 22:35

jezrael

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2 Comments

piRSquared Over a year ago

Happy holidays:-)

jezrael Over a year ago

Thank you very much, for you too ;)

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