This is a set of procedures you can use to sort lists and tables, using your own test criterion for greater/lesser comparison. It is based on the merge sort algorithm, which runs at n*log(n) speed. The procedure blocks should be draggable directly into your Blocks Editor workspace.
The logic:
function merge_sort(list m)
// Base case. A list of zero or one elements is sorted, by definition.
if length of m ≤ 1 then
return m// Recursive case. First, divide the list into equal-sized sublists // consisting of the first half and second half of the list. var left := empty list var right := empty list for each x with index i in m do if i ≤ (length of m)/2 then add x to left else add x to right // Recursively sort both sublists. left := merge_sort(left) right := merge_sort(right) // Then merge the now-sorted sublists. return merge(left, right)
Merge function logic:
function merge(left, right)
var result := empty listwhile left is not empty and right is not empty do if first(left) ≤ first(right) then append first(left) to result left := rest(left) else append first(right) to result right := rest(right) // Either left or right may have elements left; consume them. // (Only one of the following loops will actually be entered.) while left is not empty do append first(left) to result left := rest(left) while right is not empty do append first(right) to result right := rest(right) return result
