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how to use reduce in javascript

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darkstariot answered on May 21, 2020 Popularity 9/10 Helpfulness 2/10

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In JavaScript, reduce() is a built-in array method that allows you to iterate over an array and reduce it to a single value.

Here's the syntax for using reduce():

array.reduce(callback[, initialValue])

The reduce() method takes two parameters:

A callback function that is called on each element of the array.

An optional initial value that will be used as the initial value for the accumulator.

The callback function itself takes two parameters:

The accumulator - this is the value that is being accumulated as the reduce method iterates through the array.

The current value - this is the value of the current element being processed by the callback function.

Here's an example of how to use reduce() to find the sum of an array of numbers:

const numbers = [1, 2, 3, 4, 5];

const sum = numbers.reduce((accumulator, currentValue) => accumulator + currentValue);

console.log(sum); // Output: 15

In the example above, the reduce() method is called on the numbers array, and the callback function takes the accumulator and currentValue parameters. The function adds the accumulator and currentValue together on each iteration, and returns the new value of the accumulator.

The reduce() method can also be used to find the maximum or minimum value of an array, or to perform more complex operations on the array.

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Contributed on Mar 08 2023

darkstariot

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javascript reduce

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185

var array = [36, 25, 6, 15];

array.reduce(function(accumulator, currentValue) {
  return accumulator + currentValue;
}, 0); // 36 + 25 + 6 + 15 = 82

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Tags: javascript j

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Contributed on May 21 2020

TC5550

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JavaScript Reduce

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const arr = [1, 2, 3]
const result = arr.reduce((acc, curr) => acc + curr, 0)
// 1 + 2 + 3 = 6
console.log(result)

Popularity 10/10 Helpfulness 4/10 Language javascript

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Contributed on Dec 21 2022

Jozvan

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reduce javascript

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let array = [36, 25, 6, 15];
 
array.reduce((acc, curr) => acc + curr, 0)
// 36 + 25 + 6 + 15 = 82

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Contributed on Jul 05 2022

Rick Oburu

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reduce javascript

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var depthArray = [1, 2, [3, 4], 5, 6, [7, 8, 9]];

depthArray.reduce(function(flatOutput, depthItem) {
    return flatOutput.concat(depthItem);
}, []);

=> [1, 2, 3, 4, 5, 6, 7, 8, 9];


// --------------
const prices = [100, 200, 300, 400, 500];
const total = prices.reduce((total, cur) => {return total + cur} )
//  init value = 0 => total = 1500;


// --------------
const prices = [100, 200, 300, 400, 500];
const total = prices.reduce(function (total, cur) => {
                   return total + cur
                }, 1 )
// init value = 1 => so when plus all numnber will be result => 1501;

// --------------
const prices = [100, 200, 300, 400, 500];
const total = prices.reduce((total, cur) => total + cur )
// 1500;

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Contributed on Mar 03 2022

Zidane (Vi Ly - VietNam)

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javascript reduce

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const sum = array.reduce((accumulator, element) => {
  return accumulator + element;
}, 0);

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Contributed on Apr 11 2021

Cooperative Capybara

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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

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Source: blog.devgenius.io

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Contributed on Jul 10 2022

OHIOLee

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javascript reduce

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[3, 2.1, 5, 8].reduce((total, number) => total + number, 0)

// loop 1: 0 + 3
// loop 2: 3 + 2.1
// loop 3: 5.1 + 5
// loop 4: 10.1 + 8
// returns 18.1

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Source: dev.to

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Contributed on Aug 10 2021

Troubled Tiger

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reduce javascript

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 let sum = arr.reduce((curr, index) => curr + index);

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Contributed on Dec 24 2020

Frightened Frog

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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

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Contributed on Sep 03 2023

Amjad Saeed

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javascript reduce

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You can return whatever you want from reduce method, reduce array method good for computational problems
const arr = [36, 25, 6, 15];
array.reduce(function(accumulator, currentValue) {
  return accumulator + currentValue;
}, 0); // this will return Number
array.reduce(function(accumulator, currentValue) {
  return accumulator + currentValue;
}, []); // this will return array
let {total} = array.reduce(function(accumulator, currentValue) {
  let {currentVal} = currentValue
  return accumulator + currentVal;
}, {
total: 0
}); // this will return object
And one additional rule is always always retrun the first param, which do arithmetic operations.

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Contributed on Jan 13 2022

Musawir MOSA

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how to use reduce in javascript

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