OpenMusic Reference
posn-order
posn-order
(combinatorial module) -- returns an index of ordinals positions for a given sort function performed on a list
Syntax
posn-order list test
Inputs
| name | data type(s) | comments |
|---|---|---|
| list | a list or tree | |
| test | a symbol or function name or lambda function |
Output
| output | data type(s) | comments |
|---|---|---|
| first | a list of integers | the ordinal positions of the elements in the sorted list (the first is considered the 0th element. |
Description
Generates an index or ordinal positions for a given sort function. The function or symbol at test is used to sort the list, as in the sort. function. However, instead of returning the sorted list, posn- order returns an index of the operation- a list of numbers indicating the ordinal positions that the elements would have in the new list after the sorting is performed.
Examples
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Don’t forget that for all lisp functions, what we call the first element in a list is considered to be at position 0, i.e. to be the 0th element. What we call the second element of the list is in position 1, i.e. the “first” element of the list, and so on.
—|—
Using posn-order
The list (1 5 6 2 3 4) is passed to posn-order . The result of the sort would normally be (1 2 3 4 5 6).
This means that the element in position 0, 1, would stay in place, occupying the 0th place in the sorted list. The next element of the original, 5, would occupy position 4 in the sorted list. The next element of the original, 6, would occupy position 5 of the sorted list, and so on. These are the value returned by the function:
? OM->(0 4 5 1 2 3)
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