binary-sortable-hash

binary-sortable-hash

Hash arrays of numbers into a binary string from which you can reconstruct the original values, with configurable precision loss. The generated hashes sort well, so similar input values cause large shared prefixes in hashes. (as seen in geohashing)

sortable.encode([0]) === '011111111111111111111111111111111111111111111111111111111111';
sortable.decode(011111111111111111111111111111111111111111111111111111111111, 1) === -8.673617379884035e-17
sortable.encode([10, 11, -10]) === '110001001001110110011001100100001011100110001001100110011011';

Usage

Hash a lat/lon array representing Röcken Germany

[10, -10, 10] and then restore it, using different hash sizes.

var sortable = require('sortable-hash');

var rocken = {lat: 51.2408, lon: 12.1161}
//normalize scalars to +-100
var normalized = [100*rocken.lat/180, 100*rocken.lon/90]

var hash = sortable.encode(normalized)
// => '110010010010000100101111010001010001001110011100001100111111'

sortable.decode(hash, 2);
// => [ 51.24080015346408, 12.116099959239364 ]

var lowerFidelityHash = sortable.encode(normalized, 10)
// => 1100100100
sortable.decode(lowerFidelityHash, 2)
// => [50.625, 14.0625]

var hexadecimalHash = parseInt(hash, 2).toString(16)
// => c9212f45139c300 (limited precision beyond 53bits)

note: If you need precision when converting integers above 53 bits consider using bigint

API

sortable.encode(values[, options])

Hash the array values, which may only contain Numbers in the range of [-100, 100].

options can either be an object with these possible keys:

• precision: Number of bits (read: length) of the resulting binary hash

or a Number, in which case it sets options.precision.

sortable.decode(string, options)

Decode string into an Array of Numbers.

options can either be an object with these possible keys:

• num: number of elements initially passed to hash.encode. (required)

Or a Number, in which case it sets options.num

Installation

With npm do:

$ npm install binary-sortable-hash

Kudos

This is the idea of geohashes generalized for use with all numeric data and numbers of input fields.

binary-sortable-hash is a derivative of the awesome sortable-hash by @juliangrubber