# a random vector of categories
ca <- sample(c("A","B","C"), 1e6, TRUE, c(0.05, 0.9, 0.05))
# a vector of p-values, with different distribution depending on the strata
p <- runif(1e6)**ifelse(ca == "A", .8, ifelse(ca == "B", 1, 1.2))
qqplot.pvalues(p, ca)
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