CODEWITHSUNDEEP
rr-s4
Alex
Alex

Reputation: 1994

R: get value of a slot from S4 object(ScalarIndependenceTest)

I'm not an advanced user of R.Anyway I just want to do a Wilcox test on two datasets:

library(coin)
GroupA = c(2,4,3,1,2,3,3,2,3,1)
GroupB = c(3,5,4,2,4,3,5,5,3,2)
g = factor(c(rep("GroupA", length(GroupA)), rep("GroupB", length(GroupB))))
v = c(GroupA, GroupB)
ss = wilcox_test(v ~ g, distribution="exact")

What I want is to get the Zvalue and compute the effect size. ss is a S4 object, when I print it I see it reports a Z value, but I can not find it in ss@statistic. The only slot that has the value which I expect is 'test statistic', but even if this is the z-value of the test when I do :

slot(ss, 'teststatistic')

I get the error :

no slot of name "teststatistic" for this object of class "ScalarIndependenceTest"

Can anyone please give me a hint?Thanks

Upvotes: 1

Views: 1365

Answers (1)

nrussell
nrussell

Reputation: 18602

The print equivalent for S4 classes is the show method, which can be inspected using getMethod. In this case, 

ss
#
#   Exact Wilcoxon-Mann-Whitney Test
#
#data:  v by g (GroupA, GroupB)
#Z = -2.1095, p-value = 0.0385
#alternative hypothesis: true mu is not equal to 0

getMethod("show","ScalarIndependenceTest")
#Method Definition:
#
# function (object) 
# {
#     distname <- switch(class(object@distribution), AsymptNullDistribution = "Asymptotic", 
#         ApproxNullDistribution = "Approximative", ExactNullDistribution = "Exact")
#     RET <- list(statistic = setNames(object@statistic@teststatistic, 
#         nm = "Z"), p.value = object@distribution@pvalue(object@statistic@teststatistic), 
#         alternative = object@statistic@alternative, data.name = varnames(object@statistic), 
#         method = paste(distname, object@method))
#...
#...
# }

ss@statistic@teststatistic
#   GroupA 
#-2.109531 

ss@distribution@pvalue(ss@statistic@teststatistic)
#[1] 0.03850484

Upvotes: 1

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