[R] scoping problem?

[Thomas Lumley]

On Thu, 21 Jan 1999 yudi at hermes.ucd.ie wrote:

> Dear R-helpers: (this is part of a bigger program)
> the following fails as a function, but runs OK 
> if we comment out the  fnfn_ function()  line.
> Any hint would be appreciated.  -Yudi-
> 
> R : Copyright 1998, The R Development Core Team
> Version 0.63.0 Beta (Nov 13, 1998) -- on WIndows3.11
> 
> fnfn _ function (m=10,n=10,spar=2)
> {
> fn _ function(u,v){
>      uc_ u-floor(m/2)-1
>      vc_ v-floor(n/2)-1
>      exp(-(uc^2 + vc^2)/2/spar^2)
>      }
>  x1_ 1:m ; x2_ 1:n
>  x12 _ outer(x1,x2,FUN='fn')
>  filt _ x12/sum(x12)
>  image(filt)
> }

In both an old and the current development release you can fix this by
removing the quotes around 'fn', or by using FUN=get("fn",mode="function")

The problem is in outer(), in either the original or the current improved
version. If FUN is a string we use get(FUN,mode="function"), which looks
for FUN in the current environment and all parent environments. The
problem is that "current" here means the environment in outer() or in
match.fun(), not the environment outer() was called from. 

We probably need to fix match.fun() to take an environment parameter and
outer() to then use match.fun(FUN,env=sys.frame(sys.parent()))


Thomas Lumley
Assistant Professor, Biostatistics
University of Washington, Seattle.





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