Custom Permutation Generator

Usage

1.1. require

const CustomPermutation = require('custom-permutation');

1.2. import

import CustomPermutation from 'custom-permutation';

2. Constructor

CustomPermutation(
    elList:[],
    choices:{ index: [] },
    nonChoices:{ index: [] }
)

3. Usage explanied

example:

CustomPermutation(['a', 'b', 'c'], { '1': ['a', 'b'] }, { '0': ['a'] });

Permutate 3 elements which are "a", "b" and "c" with below rules

choices rule:

{ "1": ["a", "b"] }

At index=1 there can only be the element "a" or "b"

nonChoices rule:

{ "0": ["a"] }

At index=0 there can NOT be the element "a"

Note: given index are considered as 0 based: [index=0, index=1, etc.]

index	all options	after customization
0	"a", "b", "c"	"b", "c"
1	"a", "b", "c"	"a", "b"
2	"a", "b", "c"	"a", "b", "c"

4. Result set explanation:

Let's check all permutations, and see which ones are and are not valid.

Permutation	Is valid	Violates	Description
["a", "b", "c"]	No	nonChoices	first elemen can't be "a"
["a", "c", "b"]	No	nonChoices	first elemen can't be "a"
["b", "a", "c"]	Yes	-	-
["b", "c", "a"]	No	choices	second element is asked to be "a" or "b"
["c", "a", "b"]	Yes	-	-
["c", "b", "a"]	Yes	-	-

So there are just 3 results that chould be generated with these parameters.

5. Complete example

5.1. Create object from CustomPermutation class

let customPerm = new CustomPermutation(['a', 'b', 'c'], { '1': ['a', 'b'] }, { '0': ['a'] });

5.2. Get next value

5.2.1. With next

let next = customPerm.next();

while (next) {
  console.log(next);
  next = customPerm.next();
}

5.2.2. With generator

let generator = customPerm.generator();
let next = generator.next();

while (!next.done) {
  console.log(next.value);
  next = generator.next();
}

Output:

["b", "a", "c"]
["c", "a", "b"]
["c", "b", "a"]

Fixed bugs

11.06.2026 - Better typing implemented and more test coverage added. 23.09.2024 - Edge cases are handled and the codespace is simplified. 25.09.2023 - unChoices did not reflect always, fixed now.