Thanks. But aggregate will work on rows or columns.  I need to calculate mean 
for subsets of rows in a matrix
I.E.

Indx     x1     x2      x3       x4     x5      x6      x7      x8      x9
1       25      30      15      8       12      9       18      21      89
2       52      35      42      74      65      20      28      32      12
3       12      35      33      88      12      52      32      32      18
4       25      25      16      23      89      21      21      21      42
........................................
...................................
I would like to calculate means for x1-x3, x4-x6, x7-x9
For each row.

-Sohail


-----Original Message-----
From: John Kane [mailto:jrkrid...@inbox.com] 
Sent: Friday, November 16, 2012 4:35 PM
To: Khan, Sohail; 'r-help@r-project.org'
Subject: RE: [R] Calculateing means

?aggregate will do it.

x <- data.frame( height= c(50, 174, 145, 200, 210, 140, 175), 
age_group=c(1,2,2,1,1,2,1), 
                     ville= c(1,2,3,1,2,3,1))

aggregate(x$height,list(x$age_group, x$ville), mean)

or have a look at the plyr or datatable packages.

John Kane
Kingston ON Canada


> -----Original Message-----
> From: skha...@nshs.edu
> Sent: Fri, 16 Nov 2012 15:58:17 -0500
> To: r-help@r-project.org
> Subject: [R] Calculateing means
> 
> 
> Dear List,
> 
> I have a data matrix with 570 columns containing 95 (samples) with 6 
> replicates each.
> How can I calculate the mean of the replicates for 95 samples?
> Thank you.
> 
> 
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