R help - Apr 2009 - Trouble extracting graphic results from a bootstrap

Hi,

I'm trying to extract a histogram over the results from a bootstrap. However
I keep receiving the error message "Error in hist.default(boot.lrtest$ll,
breaks = "scott") : 'x' must be numeric".
The bootstrap I'm running looks like:
> boot.test <- function(data, indeces, maxit=20) {
+ y1 <- fit1+e1[indeces]
+ mod1 <- glm(y1 ~ X1-1, maxit=maxit)
+ y2 <- fit2+e2[indeces]
+ mod2 <- glm(y2~1, maxit=maxit)
+ ll <- 2*(logLik(mod1)-logLik(mod2))
+ ll
+ }
> boot.lrtest <- boot(data=M1, statistic=boot.test, R=2000, maxit=100);
> hist(boot.lrtest$ll, breaks="scott")  # This results in the error
message
stated above

So my question is: what am I doing wrong?

//Anders

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On Apr 3, 2009, at 7:10 AM, Anders Bjorn wrote:
> Hi,
>
> I'm trying to extract a histogram over the results from a bootstrap.  
> However
> I keep receiving the error message "Error in hist.default(boot.lrtest 
> $ll,
> breaks = "scott") : 'x' must be numeric".
> The bootstrap I'm running looks like:
>
>> boot.test <- function(data, indeces, maxit=20) {
> + y1 <- fit1+e1[indeces]
> + mod1 <- glm(y1 ~ X1-1, maxit=maxit)
> + y2 <- fit2+e2[indeces]
> + mod2 <- glm(y2~1, maxit=maxit)
> + ll <- 2*(logLik(mod1)-logLik(mod2))
> + ll
> + }
>> boot.lrtest <- boot(data=M1, statistic=boot.test, R=2000,
maxit=100);
>
>> hist(boot.lrtest$ll, breaks="scott")  # This results in the
error
>> message
> stated above
>
> So my question is: what am I doing wrong?
At least two things, possibly 3 or 4:
1) not specifying from which package the function "boot" comes from,  
and ..
2) not offering a reproducible example. and possibly ..
3) assuming that boot.lrtest$ll will have any meaning, with the  
corollary..
4) not looking at boot.lrtest$ll with the str function.

Regarding 3), when I look at the documentation for boot in package  
boot, I see no component of the value returned from a boot call that  
has the name "ll". The name "ll" will be thrown away after
the
function call and you need to refer to components of the boot object  
by the names that the developers used.

-- 
David Winsemius, MD
Heritage Laboratories
West Hartford, CT