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

From: Peter Dalgaard <>
Date: Tue 08 Aug 2006 - 06:14:05 EST

"Mark Na" <> writes:

> 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?

Doesn't sound like a merge problem. Will this do it?:

first[first$ID %in% second$ID,]

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  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
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Received on Tue Aug 08 11:39:04 2006

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