iterators

TypeScript library of various array iterators with reverse and rotation.

why?

Originally a proof of concept that matrix rotation can be done by transforming the matrix iterators, leaving the original data intact. It is implemented for 2D arrays ("bitmaps") but there is no general n-dimension array solution yet.

These iterators support the "for (const x in iterator) {...}" syntax. This is great since now these can be used in reactive template for loops (eg. svelte).

contents

ArrayAxisIterator

Iterates an array over one axis (dimension), eg. iterate a column in a 2D array. Not recursive, emits T items.

const anyArray3X3 = [
  [1, 2, 3],
  [4, 5, 6],
  [7, 8, 9],
];
const iterator = new ArrayDimensionIterator(anyArray3X3, [null, 1]);
for (const i of iterator) console.log(i); // 2, 5, 8

ArrayIterator

Recursively iterates arrays (ReadonlyArray types) of any number of dimensions. Needs one loop per dimension when iterating. Compatible with frontend template loops.

const arr = [1, 2, 3, 4, 5];
const iterator = new ArrayIterator(arr);
for (const item of iterator) console.log(item); // 1, 2, 3, 4, 5
for (const item of iterator.reverse()) console.log(item); // 5, 4, 3, 2, 1

For >2D arrays, it yields partial iterators recursively. Eg, when the yielded item is an array too, then another partial ArrayIterator is returned which iterates over that array.

const arr = [[1, 2, 3], [4, 5,6]];
const iterator = new ArrayIterator(arr);
for (const row of iterator) { 
  for (const item of iterator) {
    console.log(item); // 1, 2, 3, 4, 5, 6
}} 
for (const row of iterator.reverse()) { 
  for (const item of iterator) {
    console.log(item); // 4, 5, 6, 1, 2, 3
}} 
for (const row of iterator) { 
  for (const item of iterator.reverse()) {
    console.log(item); // 3, 2, 1, 6, 5, 4
}} 

ArrayIterator2D

Can handle (at least) 2D data. Provides rotating (by 90 degrees). Useful for displaying some grid or table (eg. rotating blocks in tetris). Current version still extracts columns with 90 and 270 degree rotations.

const arr = [[1, 2, 3], [4, 5, 6]];
const iterator = new ArrayIterator2D(arr).rotate();
for (const row of iterator) {
  for (const item of iterator) {
    console.log(item); // 4, 1, 5, 2, 6, 3
  }}

FlatteningIterator

Recursively iterates arrays (ReadonlyArray types) of any number of dimensions, but can be iterated in a single loop. Supports mappers for transformations etc.

Yields IterationItem items which contain the indices ("coordinates") per dimension along with the value. Looping this way might result in more readable code, and, can reduce cyclomatic complexity.

const arr = [[4, 5], [14, 15], [24, 25]];
const iterator = new FlatteningIterator(arr);
console.log(...iterator);

// { x: 0, y: 0, value: 4 }
// { x: 0, y: 1, value: 5 }
// { x: 1, y: 0, value: 14 }
// { x: 1, y: 1, value: 15 } 
// { x: 2, y: 0, value: 24 } 
// { x: 2, y: 1, value: 25 }

Mappers for FlatteningIterator

IteratorMappers object holds various mappers, which can be used with the FlatteningIterator.

import {onlyTheValue, rotateCoords} from "./IteratorMappers";

const arr = [[4, 5], [14, 15], [24, 25]];
const iterator = new FlatteningIterator(arr);
const iterator2 = iterator.with(scale(2));
iterator.use(onlyTheValue);
console.log(...iterator); // 4, 5, 14, 15, 24, 25
console.log(...iterator2); // 8, 10, 28, 30, 48, 50

Custom mappers

Functions or arrow functions can be used for custom mappers. Functions will be bound to the iterator object when executing.

import {IterationItem} from "./IterationItem";
import FlatteningIterator from "./FlatteningIterator";

const arr = [[4, 5], [14, 15], [24, 25]];
const iterator = new FlatteningIterator<number>(arr).with(
  (this: FlatteningIterator<number>, each: IterationItem<number>) => {
    // expect(this).toBeInstanceOf(FlatteningIterator);
    return each;
  }
);
console.log(...iterator);
// { x: 0, y: 0, value: 4 }
// { x: 0, y: 1, value: 5 }
// { x: 1, y: 0, value: 14 }
// { x: 1, y: 1, value: 15 } 
// { x: 2, y: 0, value: 24 } 
// { x: 2, y: 1, value: 25 }