Useful functions for working with arrays

- array-functions.md

Array functions

Useful functions for working with arrays:

• Range
• Flatten (recursively)
• Chunk
• Remove duplicates
• Remove duplicates by object property
• Group by object property

chunk.js

function chunk (arr, size) {
  return arr
    .reduce((acc, _, i) =>
      (i % size)
        ? acc
        : [...acc, arr.slice(i, i + size)]
    , [])
}

// USAGE
const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
const result = chunk(numbers, 3)

console.log(result)
// [[1, 2, 3], [4, 5, 6], [7, 8, 9], [10]]

flatten-recursively.js

function flatten (arr) {
  return arr
    .reduce((acc, cur) =>
      Array.isArray(cur)
        ? acc.concat(flatten(cur))
        : acc.concat(cur)
    , [])
}

// USAGE
const fruits = ['apple', ['pear', ['kiwi', 'orange']], ['melon']]
const result = flatten(fruits)

console.log(result)
// ['apple', 'pear', 'kiwi', 'orange', 'melon']

group-by-object-property.js

function groupByObjectProp (arr, prop) {
  return arr
    .reduce((acc, cur) => {
      const key = cur[prop]
      acc[key] = acc[key] || []
      acc[key].push(cur)
      return acc
    }, {})
}

// USAGE
const foods = [
  { name: 'apple',    category: 'fruits'     },
  { name: 'pear',     category: 'fruits'     },
  { name: 'broccoli', category: 'vegetables' },
  { name: 'potato',   category: 'vegetables' },
  { name: 'almond',   category: 'nuts'       },
  { name: 'kiwi',     category: 'fruits'     },
  { name: 'orange',   category: 'fruits'     },
  { name: 'cabbage',  category: 'vegetables' },
  { name: 'melon',    category: 'fruits'     },
  { name: 'peacan',   category: 'nuts'       },
  { name: 'walnut',   category: 'nuts'       }
]

const result = groupByObjectProp(foods, 'category')

console.log(result)
/*
{
  fruit: [
    { name: 'apple',  category: 'fruits' },
    { name: 'pear',   category: 'fruits' },
    { name: 'kiwi',   category: 'fruits' },
    { name: 'orange', category: 'fruits' },
    { name: 'melon',  category: 'fruits' }
  ],
  vegetable: [
    { name: 'broccoli', category: 'vegetables' },
    { name: 'potato',   category: 'vegetables' },
    { name: 'cabbage',  category: 'vegetables' }
  ],
  nut: [
    { name: 'almond', category: 'nuts' },
    { name: 'peacan', category: 'nuts' },
    { name: 'walnut', category: 'nuts' }
  ]
}
*/

range.js

function range (start, end) {
  return Array(end - start + 1)
    .fill()
    .map((_, i) => i + start)
}

function range2 (start, end) {
  return Array.from(
    { length: end - start + 1 },
    (_, i) => i + start
  )
}

function range3 (start, end) {
  return [...Array(end - start + 1).keys()]
    .map((_, i) => i + start)
}

// USAGE
const result = range(5, 10)

console.log(result)
// [5, 6, 7, 8, 9, 10]

remove-duplicates-by-object-property.js

function removeDupsByObjectProp (arr, prop) {
  return arr
    .filter((item, i, self) =>
      i === self.findIndex(found => found[prop] === item[prop])
    )
}

// USAGE
const foods = [
  { name: 'apple',    category: 'fruits'     },
  { name: 'apple',    category: 'fruits'     },
  { name: 'apple',    category: 'fruits'     },
  { name: 'pear',     category: 'fruits'     },
  { name: 'kiwi',     category: 'fruits'     },
  { name: 'kiwi',     category: 'fruits'     },
  { name: 'broccoli', category: 'vegetables' },
  { name: 'broccoli', category: 'vegetables' },
  { name: 'potato',   category: 'vegetables' }
]

const result = removeDupsByObjectProp(foods, 'name')

console.log(result)
/*
[
  { name: 'apple',    category: 'fruits'     },
  { name: 'pear',     category: 'fruits'     },
  { name: 'kiwi',     category: 'fruits'     },
  { name: 'broccoli', category: 'vegetables' },
  { name: 'potato',   category: 'vegetables' }
]
*/

remove-duplicates.js

function removeDups (arr) {
  return arr
    .filter((item, i, self) => self.indexOf(item) === i)
}

// USAGE
const fruits = ['apple', 'apple', 'apple', 'pear', 'kiwi', 'kiwi']
const result = removeDups(fruits)

console.log(result)
// ['apple', pear', 'kiwi']