[R] Retain only those records from a dataframe that exist in another dataframe

From: Mark Na <mtb954_at_gmail.com>
Date: Tue 08 Aug 2006 - 06:05:29 EST

Dear R community,

I have two dataframes "first" and "second" which share a unique identifier.

I wish to make a new dataframe "third" retaining only the rows in "first" which also occur in "second".

I have tried using merge but can't seem to figure it out. Any ideas?



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