choicesWithNamesRectangle.R

# Like choicesWithNames(), but returns a data frame of value, label, and
# optgroup columns. This rectangular view could also be thought of as the set
# of paths into the choicesWithNames() tree.
#
# For example, given a choices argument like this:
#
#   list(a = 1, B = list(B = 2), c = list(3))
#
# choicesWithNames() would return a tree like this:
#
#   list(a = "1", B = list(B = "2"), c = "3")
#
# and choicesWithNamesRectangle() would return an equivalent "rectangular"
# representation as a data frame:
#
#   label value optgroup
#       a     1
#       B     2        B
#       c     3
choicesWithNamesRectangle <- function(choices) {

  label    <- character()
  value    <- character()
  optgroup <- character()

  choiceTree <- choicesWithNames(choices)

  for (i in seq_along(choiceTree)) {
    # If this element is a list, then it's an group. Each sub-element
    # should be added with a group name.
    if (is.list(choiceTree[[i]])) {
      for (j in seq_along(choiceTree[[i]])) {
        label[length(label)+1]       <- names(choiceTree[[i]])[[j]]
        value[length(value)+1]       <- choiceTree[[i]][[j]]
        optgroup[length(optgroup)+1] <- names(choiceTree)[[i]]
      }
    # If this element isn't a list, then it's a leaf node with no group.
    } else {
      label[length(label)+1]       <- names(choiceTree)[[i]]
      value[length(value)+1]       <- choiceTree[[i]]
      optgroup[length(optgroup)+1] <- ""
    }
  }

  data.frame(
    label = label,
    value = value,
    optgroup = optgroup,
    stringsAsFactors = FALSE,
    row.names = NULL
  )
}