R help - Apr 2005 - function corresponding to map of perl

Is there a function in R that corresponds to the
function ``map'' of perl?

It could be called like:
	vector.a <- map( vector.b, FUN, args.for.FUN )

It should execute for each element ele.b of vector.b:
	FUN( vector.b, args.for.FUN)

It should return a vector (or data.frame) of the results
of the calls of FUN.

It nearly works using:
	 apply( data.frame( vector.b ), 1, FUN, args.for.FUN )
But when FUN is called ele.b from vector.b is no known.

Thanks - Wolfram

--- In reply to: ---
>Date:    15.04.05 08:08 (+0200)
>From:    Wolfram Fischer <wolfram at fischer-zim.ch>
>Subject: [R] function corresponding to map of perl
>
> Is there a function in R that corresponds to the
> function ``map'' of perl?
> 
> It could be called like:
> 	vector.a <- map( vector.b, FUN, args.for.FUN )
> 
> It should execute for each element ele.b of vector.b:
> 	FUN( vector.b, args.for.FUN)
> 
> It should return a vector (or data.frame) of the results
> of the calls of FUN.
> 
> It nearly works using:
> 	 apply( data.frame( vector.b ), 1, FUN, args.for.FUN )
> But when FUN is called ele.b from vector.b is no known.
Here I made a mistake. I realised now that ``apply'' does the job,
e.g.
	apply( data.frame( 1:3 ), 1, paste, sep='', "X" )

Wolfram

I think you want 'sapply()'.

-roger

Wolfram Fischer wrote:
> Is there a function in R that corresponds to the
> function ``map'' of perl?
> 
> It could be called like:
> 	vector.a <- map( vector.b, FUN, args.for.FUN )
> 
> It should execute for each element ele.b of vector.b:
> 	FUN( vector.b, args.for.FUN)
> 
> It should return a vector (or data.frame) of the results
> of the calls of FUN.
> 
> It nearly works using:
> 	 apply( data.frame( vector.b ), 1, FUN, args.for.FUN )
> But when FUN is called ele.b from vector.b is no known.
> 
> Thanks - Wolfram
> 
> ______________________________________________
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> PLEASE do read the posting guide!
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> 
-- 
Roger D. Peng
http://www.biostat.jhsph.edu/~rpeng/

I defined map as follows:

map <- function(x, y, fun) {
	mymat <- matrix( c(x,y), c(length(x), 2) )
	tmat <- t(mymat)
	oldmat <- tmat
	result <- apply(tmat, 2, function(x) {fun(x[1], x[2])})
}

It seems to work (see below). Of course you can turn it into a one-liner.
> a<-c(1,2,3)
> b<-c(4,5,6)
> mysum <- function(x, y) {x + y}
> map <- function(x, y, fun) {
+ mymat <- matrix( c(x,y), c(length(x), 2) )
+ tmat <- t(mymat)
+ oldmat <- tmat
+ result <- apply(tmat, 2, function(x) {fun(x[1], x[2])})
+ }
> (test <- map(a, b, mysum))
[1] 5 7 9

> From: Fernando Saldanha
> 
> I defined map as follows:
> 
> map <- function(x, y, fun) {
> 	mymat <- matrix( c(x,y), c(length(x), 2) )
> 	tmat <- t(mymat)
> 	oldmat <- tmat
> 	result <- apply(tmat, 2, function(x) {fun(x[1], x[2])})
> }
> 
> It seems to work (see below). Of course you can turn it into 
> a one-liner.
> 
> > a<-c(1,2,3)
> > b<-c(4,5,6)
> > mysum <- function(x, y) {x + y}
> > map <- function(x, y, fun) {
> + mymat <- matrix( c(x,y), c(length(x), 2) )
> + tmat <- t(mymat)
> + oldmat <- tmat
> + result <- apply(tmat, 2, function(x) {fun(x[1], x[2])})
> + }
> > (test <- map(a, b, mysum))
> [1] 5 7 9
Maybe you're re-inventing mapply()?
> mapply(mysum, a, b)
[1] 5 7 9

Andy
>