[R] one row matrix

[Sarah Goslee]

On 11/3/06, Waverley <waverley.paloalto at gmail.com> wrote:
> Hi,

> For example:
>
> > a = matrix (12, 3, 4)
> > b = a[1,]
> > b
> [1] 12 12 12 12
>

It doesn't have anything to do with one-row matrices, at least in your example,
since that isn't what you made. Instead, you created a matrix with 3 rows,
4 columns, and all values equal to 12.

> a <- matrix(12, 3, 4)
> a
     [,1] [,2] [,3] [,4]
[1,]   12   12   12   12
[2,]   12   12   12   12
[3,]   12   12   12   12

> a[1,]
[1] 12 12 12 12

You probably intended
> a <- matrix(c(12, 3, 4), nrow=1)

> a
     [,1] [,2] [,3]
[1,]   12    3    4

But to solve what I think you were actually asking, even though it
wasn't reflected in your example... By default, R drops unused
dimensions when subsetting. You can override this behavior

> b <- a[1, ,drop=FALSE]

> b
     [,1] [,2] [,3]
[1,]   12    3    4

See:
?subset
help('[')
?matrix

Sarah
-- 
Sarah Goslee
http://www.functionaldiversity.org