[R] aggregating strings

[Bert Gunter]

You are probably going to get tons of answers, as there are many ways -- and
packages -- to do this (e.g. see packages reshape and plyr). However, you
might want to take a look at ?tapply, for which aggregate() is a wrapper,
for the basic core R approach.

Bert Gunter
Genentech Nonclinical Biostatistics

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
Behalf Of Dry, Jonathan R
Sent: Tuesday, July 28, 2009 8:35 AM
To: r-help at r-project.org
Subject: [R] aggregating strings

I am currently summarising a data set by collapsing data based on common
identifiers in a column.  I am using the 'aggregate' function to summarise
numeric columns, i.e. "aggregate(dat[,3], list(dat$gene), mean)".  I also
wish to summarise text columns e.g. by concatenating values in a comma
separated list, but the aggregate function can only return scalar values and
so something like "aggregate(dat[,3], list(dat$gene), cat)" will not work.
Is there a simple function like aggregate that works for strings in R?

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