[R] outer() problem

[Berend Hasselman]

On 01-05-2014, at 08:44, Marc Girondot <marc_grt at yahoo.fr> wrote:

> Dear list-members,
> 
> Can someone explains me why the last command gives an error. Thanks a lot:
> > outer(0:1, 0:1, FUN=function(x, y) {x+y})
>     [,1] [,2]
> [1,]    0    1
> [2,]    1    2
> > outer(0:1, 0:1, FUN=function(x, y) {x})
>     [,1] [,2]
> [1,]    0    0
> [2,]    1    1
> > outer(0:1, 0:1, FUN=function(x, y) {1})
> Erreur dans outer(0:1, 0:1, FUN = function(x, y) { :
>  dims [produit 4] ne correspond pas à la longueur de l'objet [1]
> 
> Of course I simplify a lot my problem.

As the documentation for outer says the function arguments x and y are vectors not scalars.
Try this to see that

outer(0:1, 0:1, FUN=function(x, y) {print(x);x}) 
outer(0:1, 0:1, FUN=function(x, y) {print(x);print(y);x}) 

You are returning a scalar whereas outer expects the function to return a vector of the correct length.

A possible solution would be

outer(0:1, 0:1, FUN=function(x, y) {1+0*x}) 
outer(0:1, 0:1, FUN=function(x, y) {rep(1,length(x))}) 

Berend