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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
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    try df1.merge(df2, left_on='id', right_on='sameid') Commented Dec 21, 2015 at 21:50

1 Answer 1

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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')
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