R help - Jul 2009 - Simply matrix slice question

Is there any way to force a slice of a matrix to stay a matrix? R  
tends to convert a single row of a matrix into a vector.

Example:

z<-matrix (rnorm(20), ncol=5)
zz<-z[1,]
is.matrix(zz) #FALSE

I usually resort to:

zz<-matrix(z[1,], ncol=dim(z)[2], dimnames=list(rownames(z)[1],  
colnames(z)))

But that seems horribly kludgy.

Thanks!

-Jim

yes, you need to use the 'drop' argument; have a look at the help file 
?"[" and then try this:

z <- matrix(rnorm(20), ncol = 5)
z[1, , drop = FALSE]
z[, 1, drop = FALSE]


I hope it helps.

Best,
Dimitris


Jim Nemesh wrote:
> Is there any way to force a slice of a matrix to stay a matrix? R tends 
> to convert a single row of a matrix into a vector.
> 
> Example:
> 
> z<-matrix (rnorm(20), ncol=5)
> zz<-z[1,]
> is.matrix(zz) #FALSE
> 
> I usually resort to:
> 
> zz<-matrix(z[1,], ncol=dim(z)[2], dimnames=list(rownames(z)[1], 
> colnames(z)))
> 
> But that seems horribly kludgy.
> 
> Thanks!
> 
> -Jim
> 
> ______________________________________________
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> 
-- 
Dimitris Rizopoulos
Assistant Professor
Department of Biostatistics
Erasmus University Medical Center

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