https://github.com/mablay/gaps-islands

finds gaps and islands in an array of ranges
https://github.com/mablay/gaps-islands

Last synced: 8 days ago
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finds gaps and islands in an array of ranges

• Host: GitHub
• URL: https://github.com/mablay/gaps-islands
• Owner: mablay
• Created: 2022-09-08T22:18:17.000Z (about 2 years ago)
• Default Branch: main
• Last Pushed: 2022-09-12T17:14:12.000Z (about 2 years ago)
• Last Synced: 2023-11-20T11:03:40.908Z (12 months ago)
• Language: JavaScript
• Size: 23.4 KB
• Stars: 0
• Watchers: 1
• Forks: 0
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
# Gaps and Islands

Reduces ranges into gaps and islands.

```

ranges       ├─────┤       ├─┤     ├───────┤   ├──┤

                ├──────┤             ├─┤   ├────┤  

islands      ◼◼◼◼◼◼◼◼◼◼◼   ◼◼◼     ◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼◼

gaps                    └─┘   └───┘       

```

Identifying gaps and islands across overlapping ranges is a [classic SQL problem](https://medium.com/analytics-vidhya/sql-classic-problem-identifying-gaps-and-islands-across-overlapping-date-ranges-5681b5fcdb8).

This module answers the same question if your data is stored in an array instead of a database.

## Basic Usage

```js

import { findIslands, findGaps } from '@occami/gaps-islands'

const shifts = [

  { name: 'Alice', start: 2,  end: 6 },

  { name: 'Bob',   start: 4,  end: 8 },

  { name: 'Clair', start: 12, end: 16 }

]

// find overlapping ranges

console.log(findIslands(shifts))

/*[

  { start: 2, end: 8, value: [ { 'Alice', ... }, { 'Bob', ... } ] },

  { start: 12, end: 16, value: [ { 'Clair', ... } ] }

]*/

// see how start: 2 and end: 8 spans the first two 

// records, because they overlap, causing an island. 

// .value aggregates all objects from that island.

// find gaps between ranges

console.log(findGaps(shifts))

/* [{ start: 8, end: 12 }] */

```

## Advanced Usage

If you want fine control over the island reducer, you might want to use `mergeIslands`.

```js

import { mergeIslands } from '@occami/gaps-islands'

const shifts = [

  { name: 'Alice', start: 2,  end: 6 },

  { name: 'Bob',   start: 4,  end: 8 },

  { name: 'Clair', start: 12, end: 16 }

]

// reduce information into islands

// 1. copy data of interest in the range.value property.

const ranges = shifts.map(r => ({ ...r, value: r.end - r.start }))

// 2. define a reducer that merges overlapping ranges into the islands 'value' property.

const reducer = (a, b) => a.value + b.value

// 3. pass the reducer as optional argument.

console.log(mergeIslands(ranges, reducer))

/*[

  { start: 2, end: 8, value: 8 },

  { start: 12, end: 16, value: 4 }

]*/

```