# [R] matrix problem

Chuck Cleland ccleland at optonline.net
Mon Apr 21 12:04:44 CEST 2008

```On 4/21/2008 5:54 AM, William Simpson wrote:
> 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.

Does this help?

> matrix(runif(4), ncol=3, nrow=4)
[,1]       [,2]       [,3]
[1,] 0.60226296 0.60226296 0.60226296
[2,] 0.74104084 0.74104084 0.74104084
[3,] 0.70955138 0.70955138 0.70955138
[4,] 0.03136881 0.03136881 0.03136881

> matrix(runif(3), ncol=3, nrow=4, byrow=TRUE)
[,1]      [,2]      [,3]
[1,] 0.7008625 0.8348078 0.1003123
[2,] 0.7008625 0.8348078 0.1003123
[3,] 0.7008625 0.8348078 0.1003123
[4,] 0.7008625 0.8348078 0.1003123

> 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
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

--
Chuck Cleland, Ph.D.
NDRI, Inc. (www.ndri.org)
71 West 23rd Street, 8th floor
New York, NY 10010
tel: (212) 845-4495 (Tu, Th)
tel: (732) 512-0171 (M, W, F)
fax: (917) 438-0894

```