R help - Apr 2006 - error in which(): recursive default argument reference

Dear useRs,

I have written a very simple function to compute some probabilities  
on words (function is below). The function includes a which()  
statement applied to a vector of characters (word.split): sapply 
(word.split, function(x) which(letters==x)). This statement  worked  
as expected when used outside the global function :
 > word <- "hello"
 > (word.split <- unlist(strsplit(word, split=c())))
[1] "h" "e" "l" "l" "o"
 > (used.letters <- sapply(word.split, function(x) which(letters==x)))
h  e  l  l  o
8  5 12 12 15

However, when embedded in the fonction, the following error occurred :
 >  compute.word("hello")
Error in which(letters == x) : recursive default argument reference


Any insights would be helpful ...

Cheers,

Matthieu

Function :
#computes some probabilities based on (1) word frequency (word.freq),  
letters visibility(letters.vis), letters frequency(letters.freq) and  
viewing eccentricity (pos)
compute.word <- function(word, pos=X, word.freq=word.freq,  
letters=letters, letters.vis=letters.vis, letters.freq=letters.freq)
	{
		word.split <- unlist(strsplit(word, split=c()))
		
		#indexing vectors
		used.letters <- sapply(word.split, function(x) which(letters==x))
		pos <- c(1,rep(2,(length(word.split)-2)),3)
		
		letters.freq.word <- unlist(letters.freq[cbind(used.letters, pos)])
		letters.vis.word <- letters.vis[paste("X", pos,
sep=""),]
		
		#computations
		Mean.Lvis <- mean(letters.vis.word)
		Prod.Lvis <- prod(letters.vis.word)
		PosRel <- sum((word.freq/letters.freq.word)*(letters.vis.word))	
		output <- list(Mean.Lvis, Prod.Lvis, PosRel)
		names(output) <- c("Mean.Lvis", "Prod.Lvis",
"PosRel")
		return(output)
	}	



Matthieu Dubois, PH.D. Student
Cognitive Neuroscience Unit
Université catholique de Louvain
10, Place cardinal Mercier - 1348 Louvain-la-Neuve - BELGIUM

Matthieu.Dubois@psp.ucl.ac.be




	[[alternative HTML version deleted]]

'letters' is an argument to your function, with default
'letters', that it
itself.  (Default arguments are evaluated in the evaluation frame of the 
function, not in the caller.)

Try letters=base::letters in your argument list.

On Tue, 11 Apr 2006, Matthieu Dubois wrote:
> Dear useRs,
>
> I have written a very simple function to compute some probabilities
> on words (function is below). The function includes a which()
> statement applied to a vector of characters (word.split): sapply
> (word.split, function(x) which(letters==x)). This statement  worked
> as expected when used outside the global function :
> > word <- "hello"
> > (word.split <- unlist(strsplit(word, split=c())))
> [1] "h" "e" "l" "l" "o"
> > (used.letters <- sapply(word.split, function(x) which(letters==x)))
> h  e  l  l  o
> 8  5 12 12 15
>
> However, when embedded in the fonction, the following error occurred :
> >  compute.word("hello")
> Error in which(letters == x) : recursive default argument reference
>
>
> Any insights would be helpful ...
>
> Cheers,
>
> Matthieu
>
> Function :
> #computes some probabilities based on (1) word frequency (word.freq),
> letters visibility(letters.vis), letters frequency(letters.freq) and
> viewing eccentricity (pos)
> compute.word <- function(word, pos=X, word.freq=word.freq,
> letters=letters, letters.vis=letters.vis, letters.freq=letters.freq)
> 	{
> 		word.split <- unlist(strsplit(word, split=c()))
>
> 		#indexing vectors
> 		used.letters <- sapply(word.split, function(x) which(letters==x))
> 		pos <- c(1,rep(2,(length(word.split)-2)),3)
>
> 		letters.freq.word <- unlist(letters.freq[cbind(used.letters, pos)])
> 		letters.vis.word <- letters.vis[paste("X", pos,
sep=""),]
>
> 		#computations
> 		Mean.Lvis <- mean(letters.vis.word)
> 		Prod.Lvis <- prod(letters.vis.word)
> 		PosRel <- sum((word.freq/letters.freq.word)*(letters.vis.word))
> 		output <- list(Mean.Lvis, Prod.Lvis, PosRel)
> 		names(output) <- c("Mean.Lvis", "Prod.Lvis",
"PosRel")
> 		return(output)
> 	}
>
>
>
> Matthieu Dubois, PH.D. Student
> Cognitive Neuroscience Unit
> Universit? catholique de Louvain
> 10, Place cardinal Mercier - 1348 Louvain-la-Neuve - BELGIUM
>
> Matthieu.Dubois at psp.ucl.ac.be
>
>
>
>
> 	[[alternative HTML version deleted]]
>
>
-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595