Sorts the elements in a list according to a given compare function, and returns the element index numbers
(vl-sort-i list comparison-function)
Arguments
Any list.
A comparison function. This can be any function that accepts two arguments and returns T (or any non-nil value) if the first argument precedes the second in the sort order. The comparison-function value can take one of the following forms:
Return Values
A list containing the index values of the elements of list, sorted in the order specified by comparison-function. Duplicate elements will be retained in the result.
Examples
Sort a list of characters in descending order:
_$ (vl-sort-i '("a" "d" "f"
"c") '>)
(2 1 3 0)
The sorted list order is “f” “d” “c” “a”; “f” is the 3rd element (index 2) in the original list, “d” is the 2nd element (index 1) in the list, and so on.
Sort a list of numbers in ascending order:
_$ (vl-sort-i '(3 2 1 3) '<)
(2 1 3 0)
Note that both occurrences of 3 are accounted for in the result list.
Sort a list of 2D points by Y coordinate:
_$ (vl-sort-i '((1 3) (2 2) (3 1))
(function (lambda (e1 e2)
(< (cadr e1) (cadr e2)) ) ) )
(2 1 0)
Sort a list of symbols:
_$ (vl-sort-i
'(a d c b a)
'(lambda (s1 s2)
(< (vl-symbol-name s1) (vl-symbol-name s2)) ) )
(4 0 3 2 1)
Note that both a's are accounted for in the result list.