[R] Confidence intervals of G&K gamma statistics using bootstrap

[varin sacha]

Dear R-Experts,

I am trying to calculate the confidence intervals of the Goodman & Kruskal gamma statistics using bootstrap. There is no gamma function in the boot package. There is a gamma function in the base package, but it is the usual mathematical function.


So, I decide to try to calculate the confidence intervals using this site : 
http://www.statmethods.net/advstats/bootstrapping.html

I get a "normal" warning message, but my R code is not working and I don't understand where my mistake(s) is (are).
Here is the reproducible example with imaginary/fake data.

install.packages("ryouready") 
library(ryouready) 
a=c("satisfait", "pas satisfait", "tres satisfait","satisfait","tres satisfait","pas satisfait","satisfait","satisfait","tres satisfait","pas satisfait") 
b=c("grand", "petit", "petit", "grand", "petit", "grand", "grand", "petit", "petit", "grand")
x=table(a,b) 
ord.gamma(x) 
# calculate Goodman & Kruskal gamma using bootstrap 
library(boot) 
GK <- function(formula, data, indices) { 
d <- data[indices,] # allows boot to select sample 
tab <- xtabs(formula, data=d) 
stat <- ord.gamma(tab) 
return(stat)
} 
# bootstrapping with 2000 replications 
results <- boot(data=d, statistic=GK,R=2000) 
# view results 
results
plot(results) 
# get 95% confidence interval 
boot.ci(results, type="all") 

Best Regards, thanks for your precious help!

SV