R help - Apr 2004 - Evaluation of functionals

Suppose I have
    f1 <- function(x) x
    f2 <- function(x) x^2
    funlist <- list(f1,f2)
Then I would like to evaluate funlist such that when x is 10 I should get a list
with 10 and 100.

A naive way of doint this is 
    myf <- funlist[[1]]
    do.call(paste(quote(myf)), list(x=10))
    myf <- funlist[[2]]
    do.call(paste(quote(myf)), list(x=10))
- but there has to be much more elegant ways of doing this. I just can't
figure out how..

Put more generally, is there a way of making R "understand"
automatically that funlist above is really a function of x?

A related question is that of anonymous functions: how to evaluate
function(x)x^2 on x<-10 without assigning the function to a name?

Thanks in advance
Søren Højsgaard

	[[alternative HTML version deleted]]

Hi,

Once again, I think apply family is your friend. Dont forget functions are 
objects as any others:

At 09:36 5/04/2004, S??ren H??jsgaard wrote:
>Suppose I have
>     f1 <- function(x) x
>     f2 <- function(x) x^2
>     funlist <- list(f1,f2)
>Then I would like to evaluate funlist such that when x is 10 I should get 
>a list with 10 and 100.
 > lapply(funlist, FUN=function(f) f(10))
[[1]]
[1] 10

[[2]]
[1] 100

Or, better, pass the value as extra-parameter:

 > sapply(funlist, FUN=function(f,x) f(x), x=10)
[1]  10 100
>A related question is that of anonymous functions: how to evaluate
>function(x)x^2 on x<-10 without assigning the function to a name?
Here again, you can embedd the definition of your function in the [sl]apply 
code:

 > sapply(x<-10, FUN=function(x) x^2)
[1] 100


Eric


Eric Lecoutre
UCL /  Institut de Statistique
Voie du Roman Pays, 20
1348 Louvain-la-Neuve
Belgium

tel: (+32)(0)10473050
lecoutre at stat.ucl.ac.be
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If the statistics are boring, then you've got the wrong numbers. -Edward 
Tufte

> Suppose I have
 >     f1 <- function(x) x
 >     f2 <- function(x) x^2
 >     funlist <- list(f1,f2)
 > Then I would like to evaluate funlist such that when x is 10 I should 
 > get a list with 10 and 100.

How about
sapply(funlist, function(x) x(10))
?

 > A related question is that of anonymous functions: how to evaluate
 > function(x)x^2 on x<-10 without assigning the function to a name?

(function(x) x^2)(10)


Hadley

On Mon, 5 Apr 2004, S??ren H??jsgaard wrote:
> Suppose I have
>     f1 <- function(x) x
>     f2 <- function(x) x^2
>     funlist <- list(f1,f2)
> Then I would like to evaluate funlist such that when x is 10 I should get a
list with 10 and 100.
> 
> A naive way of doint this is 
>     myf <- funlist[[1]]
>     do.call(paste(quote(myf)), list(x=10))
>     myf <- funlist[[2]]
>     do.call(paste(quote(myf)), list(x=10))
> - but there has to be much more elegant ways of doing this. I just
can't
> figure out how..
lapply(funlist, function(f, x)f(x), x=10)
> Put more generally, is there a way of making R "understand"
> automatically that funlist above is really a function of x?
It isn't.  It is a list of functions of , so use lapply.
> A related question is that of anonymous functions: how to evaluate
> function(x)x^2 on x<-10 without assigning the function to a name?
> (function(x)x^2)(10)
[1] 100


-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
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