Defining functions inside loops

The try this:

s <- c( 0.2, 0.45, 0.38, 0.9)
f ?<- lapply(1:10, function(i)

+ ? ? local({
+ ? ? ? ? ? ? local_s <- s[i]
+ ? ? ? ? ? ? function(x)x^2+local_s
+ ? ? ? ? ? }))

rm(s)
f[[2]](4)

[1] 16.45

On Tue, Feb 15, 2011 at 10:53 AM, Eduardo de Oliveira Horta
<eduardo.oliveirahorta at gmail.com> wrote:

Thanks... but I guess I didn't make myself clear. What I was trying to
do was precisely to "store" inside the function the number associated
to s[i] rather than the call to s[i], such that I wouldn't need to
keep that object in subsequent function calls.

In other words, I wanted to use lapply to get functions equivalent to:
s <- c( 0.2, 0.45, 0.38, 0.9)
f <-list()
f[[1]] <- function(x) x^2+0.2
f[[2]] <- function(x) x^2+0.45
f[[3]] <- function(x) x^2+0.38
f[[4]] <- function(x) x^2+0.9

Best regards,

Eduardo


On Tue, Feb 15, 2011 at 7:20 AM, Dennis Murphy <djmuser at gmail.com> wrote:

Hi:

If you look at the error message, you'll see that you removed s before
evaluating f, and since an element of s is called in the function....

Try

s <- c( 0.2, 0.45, 0.38, 0.9)
f? <- lapply(1:10, function(i)local({ force(i) ; function(x)x^2+s[i]}))
f[[1]](s)

[1] 0.2400 0.4025 0.3444 1.0100

f is a list with 10 components, the first of which is
[[1]]
function (x)
x^2 + s[i]
<environment: 0x0000000002a26d48>

Each component occupies a different environment. To see what you get,

f[[1]](0.1)

[1] 0.21

for(i in 1:10) print(f[[i]](i))

[1] 1.2
[1] 4.45
[1] 9.38
[1] 16.9
[1] NA
[1] NA
[1] NA
[1] NA
[1] NA
[1] NA

for(i in 1:10) print(f[[i]](1))

[1] 1.2
[1] 1.45
[1] 1.38
[1] 1.9
[1] NA
[1] NA
[1] NA
[1] NA
[1] NA
[1] NA

HTH,
Dennis

On Mon, Feb 14, 2011 at 9:50 PM, Eduardo de Oliveira Horta
<eduardo.oliveirahorta at gmail.com> wrote:

Hello again.

Let me try something a little more intricate. Let's say instead of
forcing evaluation of 'i' I'd want to force evaluation of a vector;
for example:
s <- c( 0.2, 0.45, 0.38, 0.9)
f ?<- lapply(1:10, function(i)local({ force(i) ; function(x)x^2+s[i]}))
rm(s)
f[[1]](0.1)
Error in f[[1]](0.1) : object 's' not found

Any thoughts?

Best regards,

Eduardo

sessionInfo()

R version 2.11.1 (2010-05-31)
x86_64-pc-mingw32

locale:
[1] LC_COLLATE=Portuguese_Brazil.1252 ?LC_CTYPE=Portuguese_Brazil.1252
[3] LC_MONETARY=Portuguese_Brazil.1252 LC_NUMERIC=C
[5] LC_TIME=Portuguese_Brazil.1252

attached base packages:
[1] stats ? ? graphics ?grDevices utils ? ? datasets ?methods ? base

other attached packages:
[1] Revobase_4.2.0 ? RevoScaleR_1.1-1 lattice_0.19-13

loaded via a namespace (and not attached):
[1] grid_2.11.1 ? ? ? pkgXMLBuilder_1.0 revoIpe_1.0 ? ? ? tools_2.11.1
[5] XML_3.1-0

On Mon, Nov 15, 2010 at 7:10 PM, William Dunlap <wdunlap at tibco.com>
wrote:

You could make f[[i]] be function(t)t^2+i for i in 1:10
with
? ? f <- lapply(1:10, function(i)local({ force(i) ; function(x)x^2+i}))
After that we get the correct results
? ?> f[[7]](100:103)
? ?[1] 10007 10208 10411 10616
but looking at the function doesn't immdiately tell you
what 'i' is in the function
? ?> f[[7]]
? ?function (x)
? ?x^2 + i
? ?<environment: 0x19d7458>
You can find it in f[[7]]'s environment
? ?> get("i", envir=environment(f[[7]]))
? ?[1] 7

The call to force() in the call to local() is not
necessary in this case, although it can help in
other situations.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

-----Original Message-----
From: r-help-bounces at r-project.org
[mailto:r-help-bounces at r-project.org] On Behalf Of Eduardo de
Oliveira Horta
Sent: Monday, November 15, 2010 12:50 PM
To: r-help at r-project.org
Subject: [R] Defining functions inside loops

Hello,

I was trying to define a set of functions inside a loop, with
the loop index
working as a parameter for each function. Below I post a
simpler example, as
to illustrate what I was intending:

f<-list()
for (i in 1:10){
? f[[i]]<-function(t){
? ? f[[i]]<-t^2+i
? }
}
rm(i)

With that, I was expecting that f[[1]] would be a function
defined by t^2+1,
f[[2]] by t^2+2 and so on. However, the index i somehow
doesn't "get in" the
function definition on each loop, that is, the functions
f[[1]] through
f[[10]] are all defined by t^2+i. Thus, if I remove the
object i from the
workspace, I get an error when evaluating these functions.
Otherwise, if
don't remove the object i, it ends the loop with value equal
to 10 and then
f[[1]](t)=f[[2]](t)=...=f[[10]](t)=t^2+10.

I am aware that I could simply put

f<-function(u,i){
? f<-t^2+i
}

but that's really not what I want.

Any help would be appreciated. Thanks in advance,

Eduardo Horta

? ? ? [[alternative HTML version deleted]]

--
Jim Holtman
Data Munger Guru

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