[R] Equations as arguments to functions

[Michaell Taylor]

I am trying to pass an equation as an arguement to a function, which seems 
pretty straightforward given lazy evaluation.  

I constructed the following little test to make sure I sort of knew what I 
was doing:

go <- function(X,eq) { C <<- X*2; d <<- eq}
a _ rnorm(100)
go(10,eq=a[.5*length(a)]+C+1)
> C
[1] 20
> d
[1] 21.10551
> a[.5*length(a)]
[1] 0.1055086

Everything looks good - (BTW seems like a really powerful feature of R)

Now on to my code of interest, which doesn't work (shown below).

rm(list=ls())
load("datasets/citycodes")
increments _ seq(5000,100000,by=5000)
makeindex <- function(Y,eq) {
	losers _ 0; levels_0
	index _ 0; location _ 0; cutoff _0; totalapt_0; houses_0
	for (C in city[1:2]) {
		counter _ 0
		if (file.exists(paste("datasets/2000income/",C,sep=""))) {
			load(paste("datasets/2000income/",C,sep=""))
			counter _ counter+1}
		if (file.exists(paste("datasets/rents/2000",toupper(C),sep=""))) {
			load(paste("datasets/rents/2000",toupper(C),sep=""))
			counter _ counter+1}
	        if (counter== 2) {
			totrent _ 0
			totrent _ rep(rent,units)
			totrent _ totrent[!is.na(totrent)]
			income2000 _ sort(income2000)
			print(C)
			print(length(income2000))  # for debugging   - notice this works fine
			print(ls())                 # for debugging    - notice this works fine
			level _ eq		 # FAILURE POINT
			print(level)
			maxrent _ level/12*Y
			tot _ length(totrent[totrent<=maxrent])/length(totrent)
			house _ length(income2000[income2000<=level])/length(income2000)
			location _ c(location,C)
			index _ c(index,tot)
			cutoff _ c(cutoff,maxrent)
			totalapt _ c(totalapt,length(totrent))
			levels _ c(levels,level)
			houses _ c(houses,house)
			}
		if (counter<2) {losers _ cat(losers,C)}
		}
	overall _ data.frame(location,levels,index,houses,cutoff,totalapt)
	overall <<- overall[-1,]
	print(overall)
	losers <<- losers[-1]
	rm("overall","losers","level","maxrent")
	}
makeindex(.35,eq=(income2000[.33*length(income2000)]))		


***************  GIVES ********************

> source("finalindex.R")
[1] "At"
[1] 1459919
 [1] "C"          "counter"    "cutoff"     "eq"         "houses"
 [6] "income2000" "index"      "levels"     "location"   "losers"
[11] "rent"       "totalapt"   "totrent"    "units"      "Y"
[16] "yr"
Error: Object "income2000" not found

Ummm. I see it in the list which immediately preceded it.

Please notice that I put a ls() in this function just prior to the calling of 
eq so as to verify that income2000 is indeed "found".

while,

makeindex(.35,eq=(20000*.9))	

works fine.

This smells like a "I am an idiot" sort of problem.  I must be missing 
something simple.  Thanks for any help  - BTW sorry for the long post, trying 
to give sufficient data.


=========================================
Michaell Taylor, PhD
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