R help - Mar 2003 - apply() and unary operators

Hi everyone.

What's going on here?

> a <- matrix(1:4,2,2)
> a
     [,1] [,2]
[1,]    1    3
[2,]    2    4
> apply(a,2,sum)
[1] 3 7
> apply(a,2,"+")
     [,1] [,2]
[1,]    1    3
[2,]    2    4
> apply(a,1,"+")
     [,1] [,2]
[1,]    1    2
[2,]    3    4
> 
help(apply) says that "+" should be quoted but is otherwise silent on
unary operators.  I don't understand apply() here at all.

anyone?

-- 

Robin Hankin, Lecturer,
School of Geography and Environmental Science
Tamaki Campus
Private Bag 92019 Auckland
New Zealand

r.hankin at auckland.ac.nz
tel 0064-9-373-7599 x6820; FAX 0064-9-373-7042

On Thu, 13 Mar 2003, Robin Hankin wrote:
> Hi everyone.
>
> What's going on here?
>
>
> > a <- matrix(1:4,2,2)
> > a
>      [,1] [,2]
> [1,]    1    3
> [2,]    2    4
> > apply(a,2,sum)
> [1] 3 7
> > apply(a,2,"+")
>      [,1] [,2]
> [1,]    1    3
> [2,]    2    4
> > apply(a,1,"+")
>      [,1] [,2]
> [1,]    1    2
> [2,]    3    4
> >
>
> help(apply) says that "+" should be quoted but is otherwise
silent on
> unary operators.  I don't understand apply() here at all.
>
The problem is that "+" takes two arguments, but apply() gives it a
single
vector argument.  I think you are actually getting the unary "+"
function,
so  apply(a,1,"+") applies unary "+" to each row (which has
no effect) and
then sticks the results together into a matrix.

	-thomas