try this:

> mydata <- matrix(runif(5000),ncol=5)
> indices <- list(c(173, 193),
+                 c(434, 455),
+                 c(699, 724),
+                 c(955, 977))
> result <- lapply(indices, function(.indx){
+     mean(mydata[.indx[1]:.indx[2], 5])
+ })
>
>
> result
[[1]]
[1] 0.5364535
[[2]]
[1] 0.4080824
[[3]]
[1] 0.5109079
[[4]]
[1] 0.4392921
>


On Sun, Dec 27, 2009 at 9:14 AM, Edouard Tallent <tallen...@lycos.com>wrote:

> I have a 5-row matrix called “data”. There are headers.
> it look like this :
> Row 1   Row2    Row3    Row4    Row5
> Line1     …            …            …            …
> Line2     …            …            …            …
> Line3     …            …            …            …
> …
> Line 1838             …            …            …            …
>  I want to calculate several simple arithmetic means for Row5, that is from
> Line173 to Line193, from Line434 to Line455, from Line699 to Line724, from
> Line955 to Line977
>  A simple way is to individually compute these means. The first one
> (Line173 to Line193) is then obtained by :
> >mean(data[173:193,5], na.rm = TRUE)
> That’s right ! But, I aim to automate this calculation by creating a loop.
> I tried many things, but I have been unsuccessful at using the ‘for’ loop
> function.
> Please, don’t explain things too hard as it is often the case that people
> wants to help but gets into too much sophistication.
> Someone can write that little code for this example ? Or suggest functions
> ?
> Thanks for your help.
> Cheers,
> Édouard.
>
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>
> This is MIME Epilogue
>
>
> ______________________________________________
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html<http://www.r-project.org/posting-guide.html>
> and provide commented, minimal, self-contained, reproducible code.
>
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?

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