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`hierParseFormula` <-
function (formula, data)
{
lhs <- formula[[2]]
if (any(attr(terms(formula, data = data), "order") > 1))
stop("interactions are not allowed")
lhs <- as.matrix(eval(lhs, environment(formula), parent.frame()))
formula[[2]] <- NULL
rhs <- model.frame(formula, data, drop.unused.levels = TRUE)
rhs[] <- lapply(rhs, function(u) {
if (!is.factor(u))
u <- factor(u)
u
})
if (length(rhs) < 2)
stop("provide at least two-level hierarchy")
attr(rhs, "terms") <- NULL
list(lhs=lhs, rhs=rhs)
}
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