[R] assignment function

[Christian Hoffmann]

Hi,

I am trying to create the assignment function:
"substring<-" <- function(text, first, last=100000, sub) {
  if(is.character(first)) {
   if(!missing(last)) stop('wrong # arguments')
   return(sedit(text, first, sub))  
 }

  lf <- length(first)

  if(length(text)==1 && lf > 1) {
  	if(missing(last)) last <- nchar(text)
  	last <- rep(last, length=lf)
  	for(i in 1:lf) {
  	  text <- paste(if(first[i]>1) 
              substring(text, 1, first[i]-1), sub,
        	    substring(text, last[i]+1), sep='')
	    if(i < lf) {
	      j <- (i+1):lf
	      w <- nchar(sub) - (last[i]-first[i]+1)
	      first[j] <- first[j] + w  
	      last[j] <- last[j] +  w
	    }
   	}
  	return(text)
  }
  res <- paste(ifelse(first>1,substring(text, 1, first-1),''), sub,
              substring(text, last+1), sep='')
  res
}

Checking
> x <- 'this string'
> substring(x, 3, 4) <- 'IS'

will not result in
> x [1] "thIS string"

but will cry
Error in substr<-(*tmp*, 3, 4, value = "IS") : 
	unused argument(s) (value ...)

A cat(is.character(first),"\n") after the first line will not even be
executed.


Thanks for help.
--christian

Dr.sc.math.Christian W. Hoffmann
Mathematics and Statistical Computing
Landscape Modeling and Web Applications
Swiss Federal Research Institute WSL 
Zuercherstrasse 111
CH-8903 Birmensdorf, Switzerland
phone: ++41-1-739 22 77    fax: ++41-1-739 22 15
e-mail: Hoffmann at WSL.CH
www: http://www.wsl.ch/staff/christian.hoffmann/

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