[R] returning a list of functions

[Bert Gunter]

Lazy evaluation. 

Consider:

> funlist <- list()

> for (i in 1:5)funlist[[i]]<- eval(bquote(function(x)x^.(i)))

> str(funlist[[2]])
function (x)  
 - attr(*, "source")= chr "function(x)x^.(i)"

> funlist[[2]]
function(x)x^.(i)

> ## But...

> body(funlist[[2]])
x^2L

> body(funlist[[3]])
x^3L
>       
> funlist[[2]](2)
[1] 4

> funlist[[3]](2)
[1] 8

?bquote

See Bill Venables's "Programmer's Niche" Column on "Mind Your Language" in
the Vol 2/2, June 2002 R News for a fuller explanation. Note that bquote()
is just a kind of "macro-like" version of substitute(). 

Bert Gunter
Genentech Nonclinical Statistics



-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On
Behalf Of Rajat Mukherjee
Sent: Wednesday, January 27, 2010 7:37 AM
To: r-help at stat.math.ethz.ch
Subject: [R] returning a list of functions

Hi interested readers,
I have a function that creates several functions within a loop and I would
like 
them to be returned for further use as follows:

Main.Function(df,...){
# df is a multivariate data
funcList<-list(NULL)

for (i in 1:ncol(df)){
temp<-logspline(df[,i],...) # logspline density estimate
funcList[[i]]<-function(x){expression(temp,x)}
}

return(funcList)
}

I have tried this, unfortunately can't figure out why all the functions 
returned are identical.

Any help towards this will be much appreciated. Thanks.

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