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2d-array-rotation

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Readme

2d-array-rotation

rotates two-dimensional arrays clockwise

A collection of functions to rotate the values within a given two-dimensional array (i.e. an Array of Arrays) clockwise by 90, 180 or 270 degrees. Potentially useful for, say, turning around game pieces or sprites. Provided as an ES6-compatible module.

Functions

rotate
transpose
mirror
mirrorTranspose
hflip
vflip
wrappers/aliases:

Additional Notes

Source arrays are not directly modified.
Values within rows are reindexed directly from the source array, not copied or cloned. Object references will therefore remain unchanged.
Make sure that rows within arrays are all the same length. Results may be inconsistent otherwise.

Installation

npm install 2d-array-rotation
# or to install without devDependencies:
npm install 2d-array-rotation --only=production

Usage

Via ES6-style imports

import {transpose, mirror} from "2d-array-rotation";

Via standard node.js requires

const transpose = require('2d-array-rotation').transpose;
const mirror = require('2d-array-rotation').mirror;

Functions

rotate(arr, deg)

Master function that calls the others depending on the input. Rotates the given two-dimensional array by the given number of degrees.

let i = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9],
    [10, 11, 12],
    [13, 14, 15]
];
let o = rotate(i, 90);
/**
 * Result: [
 * [13, 10, 7, 4, 1],
 * [14, 11, 8, 5, 2],
 * [15, 12, 9, 6, 3]
 * ]
 */

Parameters

arr (Array): A two-dimensional array.
deg (Number): Number of degrees to rotate. Must be a multiple of 90, or an error will be thrown.

Returns

A two-dimensional Array with the values rotated; or, if rotating by 0 or 360 degrees is requested, the original arr itself without any modifications.

transpose(arr)

Flips the given array's values over its diagonal, equivalent to rotating it by 90 degrees clockwise.

let i = [
    [ 1, 2, 3 ],
    [ 4, 5, 6 ],
    [ 7, 8, 9 ]
];
let o = transpose(i);
/**
 * Result: [
 * [ 7, 4, 1 ],
 * [ 8, 5, 2 ],
 * [ 9, 6, 3 ]
 * ]
 */

Parameters

arr (Array): a two-dimensional array

Returns

The transpose of the input.

mirror(arr)

Flips the given array's values over the horizontal and vertical axes, the equivalent of rotating it 180 degrees clockwise.

let i = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9],
    [10, 11, 12]
];
let o = mirror(i);
/**
 * Result: [
 * [12, 11, 10],
 * [ 9,  8,  7],
 * [ 6,  5,  4],
 * [ 3,  2,  1]
 * ]
 */

Parameters

arr (Array): a two-dimensional array

Returns

The mirrored form of the given array.

mirrorTranspose(arr)

Flips the given array's values over its diagonal and the horizontal and vertical axes. Equivalent to rotating it 270 degrees clockwise.

let i = [
    [ 1, 2, 3 ],
    [ 4, 5, 6 ],
    [ 7, 8, 9 ]
];
let o = mirrorTranspose(i);
/**
 * Result: [
 * [ 3, 6, 9 ],
 * [ 2, 5, 8 ],
 * [ 1, 4, 7 ]
 * ]
 */

Parameters

arr (Array): a two-dimensional array

Returns

The mirrored transpose of the given array.

hflip(arr)

Bonus function -- flips the array over its horizontal axis.

let input = [
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9],
    [10, 11, 12]
];
let o = hflip(input);
/**
 * Result: [
 * [3, 2, 1],
 * [6, 5, 4],
 * [9, 8, 7],
 * [12, 11, 10],
 * ]
 */

vflip(arr)

Bonus function -- flips the array over its vertical axis.

let input = [
    [ 1, 2, 3 ],
    [ 4, 5, 6 ],
    [ 7, 8, 9 ]
];
let o = vflip(input);
/**
 * Result: [
 * [ 7, 8, 9 ],
 * [ 4, 5, 6 ],
 * [ 1, 2, 3 ]
 * ]
 */

rotate90CW(arr)

A wrapper around transpose. Usage may potentially result in more readable code.

rotate180CW(arr)

A wrapper around mirror. Usage may potentially result in more readable code.

rotate270CW(arr)

A wrapper around mirrorTranspose. Usage may potentially result in more readable code.

Testing

npm test

Credits and Licensing

Created by Jon Stout. Licensed under the MIT license.

Special Thanks To

u/Epyo on Reddit.