Adding A Specific Column from a Pandas Dataframe to Another Pandas Dataframe

Question

I am trying to add a column to a pandas dataframe (df1) that has a unique identifier ('id') column from another dataframe (df2) that has the same unique identifier ('sameid'). I have tried merge, but I need to only add one specific column ('addthiscolumn') not all of the columns. What is the best way to do this?

print df1
   'id'  'column1'
0  aaa   randomdata1
1  aab   randomdata2
2  aac   randomdata3
3  aad   randomdata4

print df2
   'sameid'  'irrelevant' 'addthiscolumn'
0   aaa        irre1       1234
1   aab        irre2       2345
2   aac        irre3       3456
3   aad        irre4       4567
4   aae        irre5       5678
5   aad        irre6       6789

Desired Result

print df1
   'id'  'column1'    'addthiscolumn'
0  aaa   randomdata1   1234
1  aab   randomdata2   2345
2  aac   randomdata3   3456
3  aad   randomdata4   4567

try df1.merge(df2, left_on='id', right_on='sameid')

EdChum
– EdChum

2015-12-21 21:50:16 +00:00
Commented Dec 21, 2015 at 21:50 — EdChum
– EdChum, Commented Dec 21, 2015 at 21:50

Alexander · Accepted Answer · 2015-12-21 23:35:03Z

3

Because you just want to merge a single column, you can select as follows:

df1.merge(df2[['sameid', 'addthiscolumn']], left_on='id', right_on='sameid')

answered Dec 21, 2015 at 23:35

Alexander

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