[R] trouble with boot ()

[Sundar Dorai-Raj]

Rogério Rosa da Silva wrote:
>     Dear members,
> 
> 
>     I am trying to use boot () to compute the distributions of a statistic
>     of a data set. The statistic is defined in the following code:
> 
>         eds<-function(x) {
>             r<-cor(x)
>             paren<-1-abs(r)/2
>             denom<-sum(sum(paren)+0.5)
>             desvio<-sd(x)
>             media<-mean(x)
>             a<-desvio/media
>             nom<-sum(a*(sum(paren)+0.5))
>             eds_abs<-nom/denom
>             print(eds_abs)
>             }
> 
>     I need to calculate the nonparametric bootstrap confidence intervals for
>     "eds_abs", but I am confuse about how I should call the second argument
>     for statistic function (). What I don't understand is where the index
>     should be set.
> 
>     I think I need to reproduce in boot () the following
>     loop:
> 
>         eds_null <- numeric(1000)
>         for (i in 1:1000) eds_null[i] <- eds (sample(x,replace=T)),
> 
>     where "x" is a data matrix (n-by-m) with n rows corresponding to
>     individual samples, and m-columns corresponding to the different
>     attributes. For example:
>                                        
> x<-data.frame(var1=c(23,657,67,89,23,657,67,89),var2=c(23,45,67,12,23,657,67,89),
> var3=c(25,2009,89,223,23,45,67,12),
> var4=c(1299,456,789,2, 23,45,67,12))
> 
>>eds(x)
>>[1] 6.738244
> 
> 
>     Thanks for your time,
> 
>     Rogério
> 


Have you read the help page for ?boot (which is part of package:boot)? 
If not, please do so as the posting guide suggests. Here's a quick fix 
for you:

eds <- function(x, rows) {
   x <- x[rows, , drop = FALSE]
   r <- cor(x)
   paren <- 1 - abs(r)/2
   denom <- sum(sum(paren) + 0.5)
   desvio <- sd(x)
   media <- mean(x)
   a <- desvio/media
   nom <- sum(a*(sum(paren) + 0.5))
   eds_abs <- nom/denom
   eds_abs
}

x <- data.frame(var1 = c(23, 657, 67, 89, 23, 657, 67, 89),
                 var2 = c(23, 45, 67, 12, 23, 657, 67, 89),
                 var3 = c(25, 2009, 89, 223, 23, 45, 67, 12),
                 var4 = c(1299, 456, 789, 2,  23, 45, 67, 12))

library(boot)
boot_eds <- boot(x, eds, R = 1000)
plot(boot_eds)
boot_eds