[R] How to manipulate data according to groups ?

[John Kane]

?aggregate

 tt <- matrix(c(rnorm(10), 1,1,2,2,1,3,3,3,3,2),
ncol=2))
 aggregate(t[,1], by=list(t[,2]), mean)
should work


--- Ng Stanley <stanleyngkl at gmail.com> wrote:

> Hi,
> 
> I have a two columns data, the first column are
> values, and second column
> are the groups. For this example, there are 3 groups
> 1,2,3.
> 
> How can I manipulate the values in the first column
> according to groups, say
> I would like to find mean, sum, and standard
> deviation for the different
> groups ? How do I plot data according to groups ?
> 
> > t <- matrix(c(rnorm(10), 1,1,2,2,1,3,3,3,3,2),
> ncol=2)
> 
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> 
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