[R] problems with outer

[Faheem Mitha]

On 7 May 2000, Peter Dalgaard BSA wrote:

> Faheem Mitha <faheem at email.unc.edu> writes:
> 
> > Note that my function tempexpbinsumsq merely exists for the purpose of
> > outer. I could have done 
> > tempmatrix <-
> > outer(x,y,function(x,y) expbinsumsq(point,pair,x,y,a,b,theta))
> > but I don't know if that would be correct usage.
> > 
> > Can someone explain what is going on? I'm at my wits end.
> 
> The thing that usually tricks beginners with outer() is that the
> function has to be vectorised. I.e. if you stick in vectors for x and
> y, you get a vector result back. Otherwise, you have to vectorise it
> yourself, e.g. if f takes scalar arguments,
> 
> f.vect <- function(x,y) sapply(seq(along=x),function(i)f(x[i],y[i]))

This is helpful. However I'd like to clarify the meaning of vectorisation
in this case.

Does a vectorised function with two arguments mean that if X, Y vectors
then f(X,Y)= (f(X_i,Y_i)), ie f(X,Y) is the vector with component
f(X_i,Y_i)?

This is what appears to be the case from the line beginning f.vect above.
In particular, this would force x and y to be the same length. If this is
not the case then I am puzzled how f.vect would be what I want.

A priori, I could have taken this to mean that f must satisfy the
following:
 
If X is a vector, and y is a scalar, then f(X,y) = (f(X_i,y)) ie f(X,y) is
the vector with components (f(X_i,y) and similarly for f(x,Y). But this is
not what you mean, is it?

Please excuse any confusion. Trying to debug stuff always wears me out, so
I am not at my best right now.

Thanks.                          Faheem.

 -- 
>    O__  ---- Peter Dalgaard             Blegdamsvej 3  
>   c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
>  (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
> ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
> 


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