array-prototype-pack

Array.prototype.pack (non-standard)

Bin packing algorithm (https://en.wikipedia.org/wiki/Bin_packing_problem)

Usage

Install

npm install array-prototype-pack

Example

require('array-prototype-pack');

var blocks = [
  { text: 'Rolly', height: 50 },
  { text: 'Golly', height: 40 },
  { text: 'Folly', height: 30 },
  { text: 'Jolly', height: 20 },
  { text: 'Holly', height: 30 },
  { text: 'Bolly', height: 30 }
];

const columns = blocks.pack(100, block => block.height, 'FFD');
console.log(columns);

// example output:
[
  [
    { text: 'Rolly', height: 50 },
    { text: 'Golly', height: 40 }
  ],
  [
    { text: 'Folly', height: 30 },
    { text: 'Holly', height: 30 },
    { text: 'Bolly', height: 30 }
  ],
  [
    { text: 'Jolly', height: 20 }
  ]
]

Parameters

Bin Max Size (optional)

Max size of any bin. If negative or falsy, it will use the default.

Default: Will use the largest size in the array.

Size Function

Function that gets the size from an object.

Default: (identity function, returns itself).

Method

Bin packing algorithm to use.

Available:

• FFD: first fit decreasing (https://en.wikipedia.org/wiki/Bin_packing_problem#First-fit_algorithm)

To be added:

• MFFD: modified first fit decreasing (https://en.wikipedia.org/wiki/Bin_packing_problem?oldformat=true#cite_ref-7)

Default: FFD (will be MFFD in later versions).

Return value

A new array of arrays containing the original array's elements.

The original array, or the elements inside will not be modified.

All references to non-primitive elements of the original array will be used in the return value.

This means:

• you can wrap a primitive in an object or array to identify the primitive.
• mutating non-primitive elements in either the original array or the returned array of arrays would mutate the other.

Example:

const original = [{ weight: 10 }, { weight: 5 }];
const result = original.pack(null, obj => obj.weight);
console.log(result); // [[{ weight: 10 }], [{ weight: 5 }]]
console.log(original); // [{ weight: 10 }, { weight: 5 }]

original[0].weight = 11;
console.log(original); // [{ weight: 11 }, { weight: 5 }]
console.log(result); // [[{ weight: 11 }], [{ weight: 5 }]]

Notes

For items with a size larger than the specified 'Bin Max Size', they will be placed in their own bin.

As FFD uses Array.sort, the result is not necessarily stable when sizes are not unique. (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/sort)