R help - Mar 2008 - 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)
	[[alternative HTML version deleted]]

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)
	[[alternative HTML version deleted]]

______________________________________________
R-help at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

?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)
> 
> 	[[alternative HTML version deleted]]
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained,
> reproducible code.
>