[R] Running cumulative sums in matrices

[ONKELINX, Thierry]

?cumsum can help you

m1 <- cbind(1:5,1:5,1:5)
m2 <- m1
 for(i in 2:ncol(m1)){
	m2[,i]=apply(m1[,1:i],1,sum)
	}
m3 <- t(apply(m1, 1, cumsum))
all.equal(m2, m3)

HTH,

Thierry
----------------------------------------------------------------------------
ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek
team Biometrie & Kwaliteitszorg
Gaverstraat 4
9500 Geraardsbergen
Belgium

Research Institute for Nature and Forest
team Biometrics & Quality Assurance
Gaverstraat 4
9500 Geraardsbergen
Belgium

tel. + 32 54/436 185
Thierry.Onkelinx op inbo.be
www.inbo.be

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~ Sir Ronald Aylmer Fisher

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> -----Oorspronkelijk bericht-----
> Van: r-help-bounces op r-project.org 
> [mailto:r-help-bounces op r-project.org] Namens Eleni Rapsomaniki
> Verzonden: woensdag 14 april 2010 14:18
> Aan: r-help op r-project.org
> Onderwerp: [R] Running cumulative sums in matrices
> 
> 
> 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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> 

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