Thanks for all the suggestions.

Cut + plotmeans (gplots) solved my problem.
> groups <- cut(t[,1],breaks=5)
> plotmeans(t[,2]~groups)

Thanks!
Federico

--- El jue, 29/10/09, Jim Lemon <jim@bitwrit.com.au> escribió:

De: Jim Lemon <jim@bitwrit.com.au>
Asunto: Re: [R] x-y plot as an histogram
Para: "Federico Abascal" <fedeabascal@yahoo.es>
CC: r-help@r-project.org
Fecha: jueves, 29 de octubre, 2009 23:29

On 10/30/2009 06:12 AM, Federico Abascal wrote:
> Hi,
> 
> I am investigating a problem for which I found no solution.
> I have a matrix with two columns. I have plotted it as an x-y plot (plot(matrix[,1],matrix[,2])
> But this is not apropriate for my purposes. I need to group the data in matrix[,1] into groups (as an histogram would do). Then I have to calculate the average of matrix[,2] for each group.
> 
> Before starting with loops and loops I would like to know if is there some way to do this easily with R.
Hi Federico,
If I understand your problem, I think you want first to use "cut":

groups<-cut(matrix[1,],breaks=???)

where ??? is the vector of breakpoints that you want. Then you can use whatever averaging function (AVEFUN) you want with something like "by":

by(matrix[,2],groups,AVEFUN)

Jim




      
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