R help - Mar 2013 - Trouble embedding functions (e.g., deltaMethod) in other functions

Dear R community, 

I've been writing simple functions for the past year and half and have come
across a similar problem several times. The execution of a function within
my own function produces NaN's or fails to execute as intended. My conundrum
is that I can execute the function outside of my function without error, so
it's difficult for me, as a novice functioneer, to figure out what's
going
wrong. 

Here's my example for deltaMethod(): 

t <- c(0.00000, 26.24551, 61.78180, 86.88254, 221.75480)
m <- c(48.591707, 15.655895, 12.284635, 5.758547, 0.000000)
dat <- data.frame(t = t, m = m)
m0 <- m[1]
t0 <- t[5]
nlls <- nls(m ~ (m0^(1/lambda) - (t * m0/t0)^(1/lambda))^lambda, 
    start = list(lambda = 1), data = dat)
xVal <- seq(0, t0, length = 10)
mod.SE <- list()
for(i in 1:length(xVal)){
	z <- xVal[i]
	mod.SE[[i]] <- deltaMethod(nlls, "(m0^(1/lambda) - (z *
m0/t0)^(1/lambda))^lambda")$SE
}
mod.SE

This code executes deltaMethod() flawlessly (NOTE: [[1]] and [[10]] are
supposed to be NaN's). However, my goal is to embed the deltaMethod inside
another function I'm writing. For brevity's sake, here's a very
simple
example that produces the same problem.

deltaSE <- function(mod, x){	
	mod.SE <- list()
	for(i in 1:length(xVal)){
		z <- xVal[i]
		mod.SE[[i]] <- deltaMethod(mod, "(m0^(1/lambda) - (z *
m0/t0)^(1/lambda))^lambda")$SE
	}
	mod.SE
}
deltaSE(nlls, xVal)

deltaMethod, when embedded in my deltaSE function produces only NaN's.  When
I debug(deltaSE) and debug(deltaMethod), and then debug(deltaMethod.default)
once delta method is debugging within deltaSE, I can see that eval() is
producing a value of 0 for the estimate value of m. An m of 0 indeed would
produce an NaN. I'm just not sure why this function is performing
differently inside and outside my function. 

Any help for a lowly functioneer would be great!
Patrick



--
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http://r.789695.n4.nabble.com/Trouble-embedding-functions-e-g-deltaMethod-in-other-functions-tp4662178.html
Sent from the R help mailing list archive at Nabble.com.

Here is what you sent:

deltaSE <- function(mod, x){
        mod.SE <- list()
        for(i in 1:length(xVal)){
                z <- xVal[i]
                mod.SE[[i]] <- deltaMethod(mod, "(m0^(1/lambda) - (z *
m0/t0)^(1/lambda))^lambda")$SE
        }
        mod.SE
}
deltaSE(nlls, xVal)

but within the function, there is no 'xVal'; did you really mean
'x' as in:

deltaSE <- function(mod, x){
        mod.SE <- list()
        for(i in 1:length(x)){
                z <- x[i]
                mod.SE[[i]] <- deltaMethod(mod, "(m0^(1/lambda) - (z *
m0/t0)^(1/lambda))^lambda")$SE
        }
        mod.SE
}
deltaSE(nlls, xVal)

On Fri, Mar 22, 2013 at 7:28 AM, PatGauthier <pgauthi1@lakeheadu.ca>
wrote:
> Dear R community,
>
> I've been writing simple functions for the past year and half and have
come
> across a similar problem several times. The execution of a function within
> my own function produces NaN's or fails to execute as intended. My
> conundrum
> is that I can execute the function outside of my function without error, so
> it's difficult for me, as a novice functioneer, to figure out
what's going
> wrong.
>
> Here's my example for deltaMethod():
>
> t <- c(0.00000, 26.24551, 61.78180, 86.88254, 221.75480)
> m <- c(48.591707, 15.655895, 12.284635, 5.758547, 0.000000)
> dat <- data.frame(t = t, m = m)
> m0 <- m[1]
> t0 <- t[5]
> nlls <- nls(m ~ (m0^(1/lambda) - (t * m0/t0)^(1/lambda))^lambda,
>     start = list(lambda = 1), data = dat)
> xVal <- seq(0, t0, length = 10)
> mod.SE <- list()
> for(i in 1:length(xVal)){
>         z <- xVal[i]
>         mod.SE[[i]] <- deltaMethod(nlls, "(m0^(1/lambda) - (z *
> m0/t0)^(1/lambda))^lambda")$SE
> }
> mod.SE
>
> This code executes deltaMethod() flawlessly (NOTE: [[1]] and [[10]] are
> supposed to be NaN's). However, my goal is to embed the deltaMethod
inside
> another function I'm writing. For brevity's sake, here's a very
simple
> example that produces the same problem.
>
> deltaSE <- function(mod, x){
>         mod.SE <- list()
>         for(i in 1:length(xVal)){
>                 z <- xVal[i]
>                 mod.SE[[i]] <- deltaMethod(mod, "(m0^(1/lambda) -
(z *
> m0/t0)^(1/lambda))^lambda")$SE
>         }
>         mod.SE
> }
> deltaSE(nlls, xVal)
>
> deltaMethod, when embedded in my deltaSE function produces only NaN's.
>  When
> I debug(deltaSE) and debug(deltaMethod), and then
> debug(deltaMethod.default)
> once delta method is debugging within deltaSE, I can see that eval() is
> producing a value of 0 for the estimate value of m. An m of 0 indeed would
> produce an NaN. I'm just not sure why this function is performing
> differently inside and outside my function.
>
> Any help for a lowly functioneer would be great!
> Patrick
>
>
>
> --
> View this message in context:
>
http://r.789695.n4.nabble.com/Trouble-embedding-functions-e-g-deltaMethod-in-other-functions-tp4662178.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>


-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.

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