merge-k-sorted-arrays

Merges 2 or more sorted arrays efficiently using a priority queue.

See https://algorithms.tutorialhorizon.com/merge-k-sorted-arrays/ for an explanation of the algorithm.

Usage

npm install --save merge-k-sorted-arrays

Pass an array of the arrays to merge as the first argument:

var merge = require('merge-k-sorted-arrays')

merge([
  [1, 3, 5, 7],
  [2, 4, 6, 8],
  [0, 9, 10, 11],
])
// [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]

With custom comparator

You may pass an optional custom comparator:

merge(
  [
    [7, 5, 3, 1],
    [8, 6, 4, 2],
    [11, 10, 9, 0],
  ],
  { comparator: (a, b) => b - a }
)
// [11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1]

Merging parallel arrays

Let's say you want to merge arrays of times and their corresponding values. If you pass the outputMetadata: true option, merge will return [indexOfSourceArray, indexInSourceArray, value] tuples that you can use to

var times = [
  [0, 2, 4, 6],
  [1, 3, 5, 7],
]
var values = [
  [10, 20, 50, 40],
  [80, 70, 30, 60],
]

var merged = merge(times, { outputMetadata: true })

var mergedTimes = merged.map(([a, i, time]) => time)
// [0, 1, 2, 3, 4, 5, 6, 7]
var mergedValues = merged.map(([a, i]) => values[a][i])
// [10, 80, 20, 70, 50, 30, 40, 60]

Unique / Dedupe

Passing the unique: true option will exclude duplicate elements:

merge(
  [
    [1, 3, 3, 6, 6],
    [2, 2, 3, 5],
  ],
  { unique: true }
)
// [1, 2, 3, 5, 6]

When using unique: true with outputMetadata: true, the last occurrence of a value in the last array containing that value wins:

merge(
  [
    [1, 3, 3, 6, 6],
    [2, 2, 3, 5],
  ],
  { unique: true, outputMetadata: true }
)
// [
//   [0, 0, 1],
//   [1, 1, 2],
//   [1, 2, 3],
//   [1, 3, 5],
//   [0, 4, 6],
// ]