Dear Contributors,
I am asking help on the way how to solve a problem related to loops for
that I always get confused with.
I would like to perform the following procedure in a compact way.

Consider that p is a matrix composed of 100 rows and three columns. I need
to calculate the sum over some rows of each
column separately, as follows:

fa1<-(colSums(p[1:25,]))

fa2<-(colSums(p[26:50,]))

fa3<-(colSums(p[51:75,]))

fa4<-(colSums(p[76:100,]))

fa5<-(colSums(p[1:100,]))



and then I need to  apply to each of them the following:


fa1b<-c()

for (i in 1:3){

fa1b[i]<-(100-(100*abs(fa1[i]/sum(fa1[i])-(1/3))))

}


fa2b<-c()

for (i in 1:3){

fa2b[i]<-(100-(100*abs(fa2[i]/sum(fa2[i])-(1/3))))

}


and so on.

Is there a more efficient way to do this?

Thanks for your time!

Francesca

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Francesca Pancotto, PhD
Università di Modena e Reggio Emilia
Viale A. Allegri, 9
40121 Reggio Emilia
Office: +39 0522 523264
Web: https://sites.google.com/site/francescapancotto/
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