[R] Matrices with a single column

[Uwe Ligges]

Crispin Miller wrote:

> Hi,
> I've got a quick question about what happens when indexing into matrices
> with a single column. I was wondering if anyone can help ...
>  
> For example:
> 
>>x <- matrix(1:10)
> 
> 
>>y <- cbind(x,x)
> 
> 
>>x[4:6,]
> 
> 
> [1] 4 5 6
> 
> 
>>y[4:6,]
> 
> 
>    [,1] [,2]
> 
> [1,] 4 4
> 
> [2,] 5 5
> 
> [3,] 6 6
> 
> 
>>class(x[4:6,])
> 
> 
> [1] "integer"
> 
> 
>>class(y[4:6,])
> 
> 
> [1] "matrix"
> 
> It seems that R is returning the results of indexing into a matrix with
> one column as a vector rather than a matrix?
> 
> Does anyone have a good way of preventing this from happening?

Yes, the argument "drop":

x[4:6,,drop=FALSE]

Uwe Ligges

> cheers,
> 
> crispin
>  
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