# [R] Odp: matrix problem

Petr PIKAL petr.pikal at precheza.cz
Mon Apr 21 12:50:47 CEST 2008

```Hi

Not sure what you want to do.
You can set dimensions to your vector.

vec<-1:12
dim(vec)<-c(3,4)

you can repeat your vector for n times

vec<-rep(1:4,3)
dim(vec) <- c(4,3)

or you can use byrow option

vec<-1:12
matrix(vec, nrow=4, ncol=3, byrow=T)

Petr Pikal
petr.pikal at precheza.cz
724008364, 581252140, 581252257

r-help-bounces at r-project.org napsal dne 21.04.2008 11:54:03:

> Hi Everyone,
>
> I am running into a problem with matrices. I use R version 2.4.1 and
> an older version.
>
> The problem is this:
> m<-matrix(ncol=3,nrow=4)
> m[,1:3]<-runif(n=4)
>
> That does what I expect; it fills up the rows of the matrix with the
> data vector
> > m
>           [,1]      [,2]      [,3]
> [1,] 0.2083071 0.2083071 0.2083071
> [2,] 0.5865763 0.5865763 0.5865763
> [3,] 0.7901782 0.7901782 0.7901782
> [4,] 0.8298317 0.8298317 0.8298317
>
> But this doesn't work:
> m[1:4,]<-runif(n=3)
> > m
>            [,1]       [,2]       [,3]
> [1,] 0.96864939 0.11656740 0.06182311
> [2,] 0.11656740 0.06182311 0.96864939
> [3,] 0.06182311 0.96864939 0.11656740
> [4,] 0.96864939 0.11656740 0.06182311
>
> I want it to fill up the columns of the matrix with the data vector.
>
> Maybe there is a better way to do what I want. I need to do both of
> the above. The matrices are large, so I need a fast method.
>
> Thanks very much for any help.
>
> Bill Simpson
>
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