[R] Kruskal Walllis test

[Wu Gong]

The apply function coerces the factor results to a character array
apply(g,2,class) # gives character

The kruskal.test function doesn't take character vector as the group
argument.
kruskal.test(as.character(plant.height) ~ as.character(g[,8])) #doesn't work
kruskal.test(plant.height ~ as.character(g[,8])) #doesn't work
kruskal.test(as.character(plant.height) ~ g[,8]) #works

You'd better change the kw function.
kw <- function(x) kruskal.test(plant.height ~ as.factor(x))$"p.value"

-----
A R learner.
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