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
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