R help - Aug 2010 - Reducing a list of functions by composition fails

Hi All,

I'd like to be able to specify the ordered composition of several
functions. So I defined compose:

compose <- function(f,g){
  function(x){f(g(x))}
}

and some simple test functions:

plus2 <- function(x){x+2}
plus3 <- function(x){x+3}
plus4 <- function(x){x+4}
>  (compose(plus2,compose(plus3,plus4)))(3)
[1] 12

Works fine. But trying to reduce a list of functions by compose fails:
> Reduce(compose,list(plus2,plus3,plus4),right=TRUE)(3)
Error: evaluation nested too deeply: infinite recursion / options(expressions=)?

As far as I can tell, that reduction should be the same as my call
above. What am I doing wrong?

Thanks very much!

> Funcall <- function(f, ...) f(...)
> Reduce(Funcall,list(plus2,plus3,plus4),init=3,right=TRUE)
[1] 12

Basically from the examples from ?Reduce.
HTH,
David L. Reiner
XR Trading LLC

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Mog
Sent: Thursday, August 05, 2010 3:32 PM
To: r-help at r-project.org
Subject: [SPAM] - [R] Reducing a list of functions by composition fails -
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Hi All,

I'd like to be able to specify the ordered composition of several
functions. So I defined compose:

compose <- function(f,g){
  function(x){f(g(x))}
}

and some simple test functions:

plus2 <- function(x){x+2}
plus3 <- function(x){x+3}
plus4 <- function(x){x+4}
>  (compose(plus2,compose(plus3,plus4)))(3)
[1] 12

Works fine. But trying to reduce a list of functions by compose fails:
> Reduce(compose,list(plus2,plus3,plus4),right=TRUE)(3)
Error: evaluation nested too deeply: infinite recursion / options(expressions=)?

As far as I can tell, that reduction should be the same as my call
above. What am I doing wrong?

Thanks very much!

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I realize that the Funcall example with an init parameter will work,
but I'd like to be able to get a one-argument function/closure out of
that reduction, if at all possible. Sorry, I under-specified in my
question.

Thanks!

On Thu, Aug 5, 2010 at 4:31 PM, Mog <mogunus at gmail.com>
wrote:
> Hi All,
>
> I'd like to be able to specify the ordered composition of several
> functions. So I defined compose:
>
> compose <- function(f,g){
> ?function(x){f(g(x))}
> }
>
> and some simple test functions:
>
> plus2 <- function(x){x+2}
> plus3 <- function(x){x+3}
> plus4 <- function(x){x+4}
>
>> ?(compose(plus2,compose(plus3,plus4)))(3)
> [1] 12
>
> Works fine. But trying to reduce a list of functions by compose fails:
>
>> Reduce(compose,list(plus2,plus3,plus4),right=TRUE)(3)
> Error: evaluation nested too deeply: infinite recursion /
options(expressions=)?
>
> As far as I can tell, that reduction should be the same as my call
> above. What am I doing wrong?
Its due to lazy evaluation.  Insert this at the top of compose:

   force(f); force(g)

Thanks very much! Works fine now. I'll read up on R's evaluation model.