[R] [PS] How to manipulate data according to groups ?

[Ben Fairbank]

Look at ?tapply, based on your description, it is what you want.

Ben 

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Ng Stanley
Sent: Thursday, March 13, 2008 9:25 AM
To: r-help
Subject: [PS] [R] How to manipulate data according to groups ?

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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