[R] subscripting a one column matrix drops dimension

[jim holtman]

You need drop=FALSE:   see ?'['

> x<- matrix(rnorm(100), ncol=1)
> str(x)
 num [1:100, 1] -0.626  0.184 -0.836  1.595  0.330 ...
> str(x[20:30,])
 num [1:11]  0.5939  0.9190  0.7821  0.0746 -1.9894 ...
> str(x[20:30,,drop=FALSE])
 num [1:11, 1]  0.5939  0.9190  0.7821  0.0746 -1.9894 ...
>


On Tue, Oct 21, 2008 at 9:24 AM, Pedroso MOACIR <moacir at supagro.inra.fr> wrote:
> Hi all,
>
> Why subscripting a one column matrix drops one dimension?
>
>> x<- matrix(rnorm(100), ncol=1)
>
>> str(x)
> num [1:100, 1] -0.413 -0.845 -1.625 -1.393  0.507 ...
>
>> str(x[20:30,])
> num [1:11] -0.315 -0.693 -0.771  0.448  0.204 ...
>
>> str(x[20:30])
> num [1:11] -0.315 -0.693 -0.771  0.448  0.204 ...
>
>
> This breaks:
>
>> cov(x)
>         [,1]
> [1,] 0.9600812
>
>> cov(x[20:30])
> Erreur dans cov(x[20:30]) : fournir 'x' et 'y' ou bien 'x' en matrice
>
>
> And this behavior is braking function clustIndex (when used with
> unidimensional data),
> from the package cclust, file Rindexes.R, lines 137-147:
>
>   ttww <- function(x, clsize, cluster)
>     {
>       n <- sum(clsize)
>       k <- length(clsize)
>       w<-0
>       tt <- cov(x)*n
>       for (l in 1:k)
>         w<- w+cov(x[cluster==l,])*clsize[l]
>       zttw <- list(tt=tt, w=w)
>       return(zttw)
>     }
>
> Any way around it?
>
> Thank you.
>
> Moacir Pedroso Jr.
> Embrapa - Empresa Brasileira de Pesquisa Agropecuária
> (on leave at INRA - Instutute National de la Recherche Agronomique)
>
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>



-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?