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array reduce method in javascript

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Amjad Saeed answered on May 6, 2020 Popularity 8/10 Helpfulness 2/10

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array reduce method in javascript

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// Certainly! The reduce() method in JavaScript is a powerful tool for iterating over an array and accumulating a single value based on the elements of that array. It takes a callback function as its argument and can be used in various ways. Here are 10 tricky questions that will help you understand and master the reduce() method:

const items = ['apple', 'banana', 'apple', 'cherry', 'banana', 'apple'];
const itemCount = items.reduce((accumulator, currentValue) => {
  accumulator[currentValue] = (accumulator[currentValue] || 0) + 1;
  return accumulator;
}, {});
console.log(itemCount); // Output: { apple: 3, banana: 2, cherry: 1 }


const nestedArray = [[1, 2], [3, 4], [5, 6]];
const flattenedArray = nestedArray.reduce((accumulator, currentValue) => accumulator.concat(currentValue), []);
console.log(flattenedArray); // Output: [1, 2, 3, 4, 5, 6]


const numbers = [1, 2, 3, 4, 5];
const sum = numbers.reduce((accumulator, currentValue) => accumulator + currentValue, 0);
console.log(sum); // Output: 15

const people = [
  { name: 'Alice', age: 25 },
  { name: 'Bob', age: 30 },
  { name: 'Charlie', age: 35 }
];

const totalAge = people.reduce((accumulator, person) => accumulator + person.age, 0);
console.log(totalAge); // Output: 90


const words = ['apple', 'banana', 'cherry', 'date', 'elderberry'];
const longestWord = words.reduce((longest, word) => (word.length > longest.length ? word : longest), '');
console.log(longestWord); // Output: 'elderberry'


const originalArray = [1, 2, 3, 4, 5];
const reversedArray = originalArray.reduce((accumulator, currentValue) => [currentValue].concat(accumulator), []);
console.log(reversedArray); // Output: [5, 4, 3, 2, 1]


const numbers = [4, 2, 9, 5, 1];
const maxNumber = numbers.reduce((max, number) => (number > max ? number : max), numbers[0]);
console.log(maxNumber); // Output: 9


const people = [
  { name: 'Alice', nationality: 'USA' },
  { name: 'Bob', nationality: 'Canada' },
  { name: 'Charlie', nationality: 'USA' }
];

const groupedByNationality = people.reduce((accumulator, person) => {
  (accumulator[person.nationality] = accumulator[person.nationality] || []).push(person);
  return accumulator;
}, {});

console.log(groupedByNationality);
/* Output:
{
  USA: [
    { name: 'Alice', nationality: 'USA' },
    { name: 'Charlie', nationality: 'USA' }
  ],
  Canada: [
    { name: 'Bob', nationality: 'Canada' }
  ]
}
*/


const functions = [
  (x) => x * 2,
  (x) => x + 3,
  (x) => x - 1
];

const initialValue = 5;

const result = functions.reduce((acc, func) => func(acc), initialValue);
console.log(result); // Output: 11

Popularity 8/10 Helpfulness 2/10 Language javascript

Source: Grepper

Tags: array-reduce javascript

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Contributed on Sep 03 2023

Amjad Saeed

0 Answers Avg Quality 2/10

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reduce function in js

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let arr = [1, 2, 3, 4, 5];
let newArr = arr.reduce((item1,item2) => {
    return item1 + item2;
})

console.log(newArr)
// output 15
// 1+2+3+4+5

Popularity 10/10 Helpfulness 4/10 Language javascript

Source: Grepper

Tags: function functio

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Contributed on Feb 09 2023

Muhammad Rayyan

0 Answers Avg Quality 2/10

Using Array.reduce() method

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// define a reusable function
const calculateSum = (arr) => {
    return arr.reduce((total, current) => {
        return total + current;
    }, 0);
}

// try it
console.log(calculateSum([1, 2, 3, 4, 5]));

Popularity 9/10 Helpfulness 3/10 Language javascript

Source: www.kindacode.com

Tags: javascript j

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Contributed on Aug 29 2022

Lucky Lizard

0 Answers Avg Quality 2/10

JavaScript Array Methods .reduce()

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const list = [1, 2, 3, 4, 5];
console.log(list.reduce((number, nextNumber) => number + nextNumber));
// --> 15

Popularity 10/10 Helpfulness 3/10 Language javascript

Source: github.com

Tags: javascript j

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Contributed on May 07 2021

Hilarious Hippopotamus

0 Answers Avg Quality 2/10

THE REDUCE() METHOD IN JAVASCRIPT

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/*
This method takes a callback that takes two parameters,
one that represents the element from the last iteration and the other is the current
element of the iteration
*/

let nums = [2,4,6,8,3,5]

let result = nums.reduce((prev,curr)=>prev+curr)
console.log(result); // 28

Popularity 10/10 Helpfulness 3/10 Language javascript

Source: blog.devgenius.io

Tags: javascript j

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Contributed on Jul 10 2022

OHIOLee

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js array reduce

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// Arrow function
reduce((previousValue, currentValue) => { /* ... */ } )
reduce((previousValue, currentValue, currentIndex) => { /* ... */ } )
reduce((previousValue, currentValue, currentIndex, array) => { /* ... */ } )
reduce((previousValue, currentValue, currentIndex, array) => { /* ... */ }, initialValue)

// Callback function
reduce(callbackFn)
reduce(callbackFn, initialValue)

// Inline callback function
reduce(function(previousValue, currentValue) { /* ... */ })
reduce(function(previousValue, currentValue, currentIndex) { /* ... */ })
reduce(function(previousValue, currentValue, currentIndex, array) { /* ... */ })
reduce(function(previousValue, currentValue, currentIndex, array) { /* ... */ }, initialValue)

Popularity 10/10 Helpfulness 3/10 Language javascript

Source: developer.mozilla.org

Tags: array-reduce array-redu

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Contributed on Feb 21 2022

Tung

0 Answers Avg Quality 2/10

javascript reduce function array

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let numbers = [1, 2, 3];
let sum = numbers.reduce(function (previousValue, currentValue) {
    return previousValue + currentValue;
});

Popularity 10/10 Helpfulness 2/10 Language javascript

Source: www.javascripttutorial.net

Tags: function functio

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Contributed on Apr 28 2022

Michael Futral

0 Answers Avg Quality 2/10

array reduce javascript

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const numbers = [260, 25, 35];

console.log(numbers.reduce(myFunc))

function myFunc(total, num) {
  return total - num;
}
/*console.log will show 200 since the first element minus 35 and minus 25 is 260-25-35=200*/
/*while the name is "reduce", you do NOT have to subtract. Reduce() is more about "take the first element as total, and do something(whatever the function says) to it for each of the remaining elements; the remaining elements will be identified as the second parameter num for the function myFunc, you do whatever once for all remaining elements*/

Popularity 10/10 Helpfulness 1/10 Language javascript

Source: Grepper

Tags: array-reduce array-redu

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Contributed on Jul 31 2022

Javasper

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reduce function javascript

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array.reduce(function(acumulador, elementoAtual, indexAtual, arrayOriginal), valorInicial)

Popularity 10/10 Helpfulness 1/10 Language javascript

Source: medium.com

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Contributed on May 06 2020

Shy Sable

0 Answers Avg Quality 2/10

JavaScript Array reduce()

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-1

const numbers = [45, 4, 9, 16, 25];
let sum = numbers.reduce(myFunction);

function myFunction(total, value, index, array) {
  return total + value;
}

Popularity 10/10 Helpfulness 1/10 Language javascript

Source: Grepper

Tags: javascript j

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Contributed on May 22 2022

naly moslih

0 Answers Avg Quality 2/10

array reduce method in javascript

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