[R] Avoiding a Loop?

[Zoltan Barta]

"Rau, Roland" <Rau at demogr.mpg.de> writes:

> Dear R-Helpers,
>
> I have a matrix where the first column is known. The second column is
> the result of multiplying this first column with a constant "const". The
> third column is the result of multiplying the second column with
> "const".....
> So far, I did it like this (as a simplified example):
>
> nr.of.columns <- 4
>
> myconstant <- 27.5
>
> mymatrix <- matrix(numeric(0), nrow=5, ncol=nr.of.columns)
>
> mymatrix[,1] <- 1:5
>
> for (i in 2:nr.of.columns) {
> 	mymatrix[,i] <- myconstant * mymatrix[,i-1]
> }
>
>
> Can anyone give me some advice whether it is possible to avoid this loop
> (and if yes: how)?
>

How about:

> myconstant <- 27.5
> a <- 1:5
> myconstant <- myconstant^((1:nr.of.columns)-1)
> myconstant
[1]     1.00    27.50   756.25 20796.88
> mymatrix <- outer(a,myconstant)
> mymatrix
     [,1]  [,2]    [,3]      [,4]
[1,]    1  27.5  756.25  20796.88
[2,]    2  55.0 1512.50  41593.75
[3,]    3  82.5 2268.75  62390.62
[4,]    4 110.0 3025.00  83187.50
[5,]    5 137.5 3781.25 103984.38
> 

HTH

Zoltan

> Any suggestions are welcome!
>
> Thanks,
> Roland
>
>
>
>
> +++++
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-- 


Z. Barta 
Dept. of Evol. Zool., Univ. of Debrecen, Debrecen, H-4010, Hungary
Phone: 36 52 316 666 ext. 2334, Fax: 36 52 533 677
E-mail: zbarta at delfin.unideb.hu, http://puma.unideb.hu/~zbarta/