Hi:

Is this what you want?

> m1=cbind(1:5,1:5,1:5)
> apply(m1, 1, cumsum)
     [,1] [,2] [,3] [,4] [,5]
[1,]    1    2    3    4    5
[2,]    2    4    6    8   10
[3,]    3    6    9   12   15


HTH,
Dennis

On Wed, Apr 14, 2010 at 5:18 AM, Eleni Rapsomaniki
<er339@medschl.cam.ac.uk>wrote:

>
> Dear R-helpers,
>
> I have a huge data-set so need to avoid for loops as much as possible. Can
> someone think how I can compute the result in the following example (that
> uses a for-loop) using some version of apply instead (or any other similarly
> super-efficient function)?
>
> example:
> #Suppose a matrix:
> m1=cbind(1:5,1:5,1:5)
>
> #The aim is to create a new matrix with every column containing the
> cumulative sum of all previous columns.
> m2=m1
> for(i in 2:ncol(m1)){
>    m2[,i]=apply(m1[,1:i],1,sum)
> }
> m2
>
> Many thanks in advance
>
> Eleni Rapsomaniki
>
> Research Associate
> Strangeways Research Laboratory
> Department of Public Health and Primary Care
> University of Cambridge
>
>
> ______________________________________________
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

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