[R] summing columns of data frame by group

bogdan romocea br44114 at gmail.com
Tue Aug 21 23:00:14 CEST 2007

Here's one way,
lapply(split(DF, your.vector), function(x) {apply(x, 2, sum)})

> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Daniel O'Shea
> Sent: Tuesday, August 21, 2007 3:53 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] summing columns of data frame by group
> I have a data frame and one separate vector that is a
> grouping variable for the data frame.  I would like to take
> all rows of the data frame belonging to each group and then
> sum the columns with out using a for statement.
> Something like: take all rows of group 1 then
> apply(group1.data,1,sum), but do this without having to do it
> separately for each group.  Any ideas?  thank you.
> Dan
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