'arg' must be NULL or a character vector

Question

Here's a prop.test function:

baby.prop.test = function (x, n, p, conf.level = 0.95) {
  # ...
  return(prop.test(x,n,p,conf.level))
  #baby.prop.test$statistic
}
# test case
baby.prop = baby.prop.test(72, 100, .7, conf.level=.99)
stopifnot(isTRUE(all.equal(as.numeric(baby.prop$statistic), .43643578)))
stopifnot(isTRUE(all.equal(as.numeric(baby.prop$p.value), .66252058)))

Here is the error:

Error in match.arg(alternative) : 
  'arg' must be NULL or a character vector

Any idea what's wrong?

Solution

According to formals(prop.test) or ?prop.test the fourth argument is called alternative and has to be a character of c("two.sided", "less", "greater"). Your fourth element is conf.level (which is the fifth of prop.test, the order matters). To "ignore" the order of arguments you have to name your arguments (at least the conf.level):

prop.test(x, n, p, conf.level=conf.level)