Reduce basics - Part 3 of Functional Programming in JavaScript
Why Stack Overflow recommends it
Stack Overflow users link it when answering beginner questions about reduce, as a clear explanation of how the accumulator and current value work.
Recommended by 5 people across 5 different months, 2016 to 2020.
What it is
A 9-minute tutorial from Fun Fun Function in which Mattias Petter Johansson explains how Array.reduce fits alongside map and filter in JavaScript and walks through a basic summing example. It is part 3 of his functional programming in JavaScript series and uses ES2015 arrow functions.
What people said
Recommends Jan van Brügge · 2016-05 · Stack Overflow · on “Javascript beginner asking for code enhancement - Biggest number task”
@Adam Rajnoha reduce calls a function recursive on an array. The first parameter is the result of all function calls ealier, the second one is the current value. Here is a very good explanation: [this video]
Recommends Kevin Lee · 2016-06 · Stack Overflow · on “How to join array of strings in Javascript”
You can also use the javascript reduce() [LINK] function as follows: var result = [result.reduce(function(previousString, currentString) { return previousString + currentString })]; For a more detailed explanation of how it works, check out this video [this video] by Mattias Petter Johansson [LINK]
Recommends Mohammad Kermani · 2016-08 · Stack Overflow · on “How do I sum total amount of array in loop?”
If you use ES6 ( ECMAScript 2015 [LINK] ), you can use the reduce [LINK] function (Great video tutorial [this video] to learn the reduce) Here is a simple example: var yourArray = [50, 60, 70, 100, 20] var sum = yourArray.reduce((a, b) => a + b, 0); console.log(sum); //Returns: 300
Recommends Radonirina Maminiaina · 2018-02 · Stack Overflow · on “Convert a simple Object to a Complex array”
Try this code sample (Old way): var res = [] var obj = { boxer: [], brabancon: [], briard: [], bulldog: [ "boston", "french" ] } for (var key in obj) { if (!obj[key].length) { res.push({ dogBreed: key }) } else { for (var i = 0; i < obj[key].length; i++) { res.push({ dogBreed: key + ' (' + obj[key][i] + ')' }) } } } console.log(res) Or Using +ES2015 with reduce or map const obj = { boxer: [], brabancon: [], briard: [], bulldog: [ "boston", "french" ] } result = Object.keys(obj).reduce((arr, key) => { if (obj[key].length) { obj[key].forEach((item) => {arr.push({dogBreed: `${key} (${item})`})}) } else { arr.push({dogBreed: key}) } return arr; }, []) console.log(result) For more information, th
Recommends Alejandro A. · 2020-12 · Stack Overflow · on “Sum values for multiple objects in the array”
That is a nice use case of how to process data in js, particularly how functions like map and reduce can help you do that processing. Which are a nice alternative to loops and iterations. Moreover, I'd advise you to do the processing in steps, as you have defined in the description. For example: const arrayA = [ {name:'a', amount: 10, serviceId: '23a', test:'SUCCESS'}, {name:'a', amount: 9, test:'FAIL'}, {name:'b', amount: 15, serviceId: '23b', test:'SUCCESS'} ] // First group the items by name const byName = arrayA.reduce((ob, item) => { if(!(item.name in ob)) ob[item.name] = [] ob[item.name].push({amount: item.amount, test: item.test}) return ob }, {}) // Then compute the total amount in e
Cites John Abraham · 2016-10 · Stack Overflow · on “How to rewrite an Array.every() in a custom Array.reduce() in javascript?”
This question is for purely for learning purposes. funfunfunction [LINK] on youtube says that Any list higher order list transformation can be written in Array.reduce() [LINK] Audio/video Reference: [this video] . Question: Purely for learning how would one rewrite Array.every() [LINK] with Array.reduce() This question stems from my previous question here [LINK] Javascript Example: var approved1 = [ { dateApproved: new Date(), id: 1, }, { dateApproved: new Date(), id: 2, } ]; var approved2 = [ { dateApproved: null, id: 1, }, { dateApproved: new Date(), id: 2, } ]; approved1.every(a => a.dateApproved != null) ? 'APPROVED' : 'PENDING' // 'APPROVED' approved2.reduce(every) ? 'APPROVED' : 'PENDING' /