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danpantry/partition.js

Last active Oct 7, 2015
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'use strict'
/**
* Partition the given list into separate groups which may be, at most, the size given.
* @param {Array<T>} list This may be any array-like object that supports indexing and has a length property
* @param {Number} size Any positive integer that is not NaN
* @return {Array<Array<T>>} A set of arrays that are sized based upon the given size. The nested arrays may be
* no larger than the given size, but **may** be smaller; there will be no empty arrays
* @throws {TypeError} If list is falsey (i.e, undefined/null)
* @throws {TypeError} If list does not have a length property
* @throws {TypeError} If size is falsey or NaN
* @throws {TypeError} If size is less than or equal to zero
*/
function partition(list, size) {
if (!list) {
throw new TypeError('list must exist')
}
if (!list.length) {
throw new TypeError('list is not an array-like object')
}
if (size === null || size === undefined || isNaN(size)) {
throw new TypeError('size is not a number')
}
if (size < 0 || size === 0) {
throw new Error('size must be greater than zero')
}
const groups = []
let currentGroup = []
for (let index = 0; index < list.length; index++) {
currentGroup.push(list[index])
if (currentGroup.length >= size || index === list.length - 1) {
groups.push(currentGroup)
currentGroup = []
}
}
return groups
}
module.exports = partition
'use strict'
const test = require('tape')
const partition = require('./partition')
const inputList = [1, 2, 3, 4, 5]
runTestCase('example 1', inputList, 2, [[1,2],[3,4],[5]])
runTestCase('example 2', inputList, 3, [[1,2,3],[4,5]])
runTestCase('example 3', inputList, 1, [[1],[2],[3],[4],[5]])
function runTestCase(name, inputList, arraySize, expectedOutput) {
test(name, function (t) {
t.plan(1)
const output = partition(inputList, arraySize)
t.deepEqual(output, expectedOutput)
})
}
test('throw if size is null', function (t) {
const boundFun = partition.bind(undefined, inputList, null)
t.throws(boundFun, TypeError)
t.end()
})
test('throw if size is undefined', function (t) {
const boundFun = partition.bind(undefined, inputList, undefined)
t.throws(boundFun, TypeError)
t.end()
})
test('throw if size is NaN', function (t) {
const boundFun = partition.bind(undefined, inputList, NaN)
t.throws(boundFun, TypeError)
t.end()
})
test('throw if size is negative', function (t) {
const boundFun = partition.bind(undefined, inputList, -5)
t.throws(boundFun, Error)
t.end()
})
test('throw if size is zero', function (t) {
// This is because it would not make sense to have a list partitioned
// into an array of zero elements. If someone wants something like that,
// they likely want to simply create empty arrays from existing elements,
// which could be done using Array.prototype.map
const boundFun = partition.bind(undefined, inputList, 0)
t.throws(boundFun, Error)
t.end()
})
test('throw if list is null', function (t) {
const boundFun = partition.bind(undefined, null, 1)
t.throws(boundFun, TypeError)
t.end()
})
test('throw if list is undefined', function (t) {
const boundFun = partition.bind(undefined, undefined, 1)
t.throws(boundFun, TypeError)
t.end()
})
test('throw if list is not an array-like object', function (t) {
const list = {
length: undefined
}
const boundFun = partition.bind(undefined, list, 1)
t.throws(boundFun, TypeError)
t.end()
})
@danpantry

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@danpantry danpantry commented Oct 7, 2015

exception handling might be a bit overkill, and honestly, the tests aren't great because some of these will throw errors anyway. For example, if we didn't check that the list was an array-like object, the code would still error when you compare list.length to the size

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