JAVASCRIPT

javascript reduce

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

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

js reduce

// syntax: array.reduce(function, accumulator-initial-value)
let array = [3, 7, 2, 9, 5]
const result = array.reduce((accumulator, currentValue, currentIndex, arr) => {
  // code
}, initialValue)

// accumulator = will store return value of the function
// currentValue = iterate through each array element
// currentIndex = index of currentValue
// arr = original array
// initialValue = set accumulator initial value

reduce javascript

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

A.reduce

const arr = [3, 5, 4, 11, 7, 22];

arr.reduce((previousValue, currentValue) => {
    return previousValue + currentValue;  // <--- 3 + 5 + 4 + 11 + 7 + 22 = 52
}, 0) 

reduce javascript

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;

reduce()

const array1 = [1, 2, 3, 4];
const reducer = (accumulator, currentValue) => accumulator + currentValue;

// 1 + 2 + 3 + 4
console.log(array1.reduce(reducer));
// expected output: 10

// 5 + 1 + 2 + 3 + 4
console.log(array1.reduce(reducer, 5));
// expected output: 15

reduce

// Array.prototype.reduce()

const array1 = [1, 2, 3, 4];
const reducer = (accumulator, currentValue) => accumulator + currentValue;

// 1 + 2 + 3 + 4
console.log(array1.reduce(reducer));
// expected output: 10

// 5 + 1 + 2 + 3 + 4
console.log(array1.reduce(reducer, 5));
// expected output: 15

javascript reduce

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

js .reducer method

const arrayOfNumbers = [1, 2, 3, 4];
 
const sum = arrayOfNumbers.reduce((accumulator, currentValue) => {  
  return accumulator + currentValue;
});
 
console.log(sum); // 10

js reduce

Sum array elements:
let myArr = [1,2,3,-1,-34,0]
return myArr.reduce((a,b) => a + b,0)

javascript reduce

[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

reduce in js

let x = [1, 2, 3]; // 2 % 2 == 0
let v = x.reduce(e => e % 2 == 0);
console.log(v) // true 
//reduce return true or false

syntax of reduce in js

[1,2,3,4,5].reduce((acc, current)=>acc+current, 0)

reduce javascript

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

.reduce javascript

reduce function sample solution

array reduce

arr.reduce(callback( accumulator, currentValue[, index[, array]] ) {
  // return result from executing something for accumulator or currentValue
}[, initialValue]);

js reduce

// 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)

reduce method

function reduce(array, combine, start) {
  let current = start;
  for (let element of array) {
    current = combine(current, element);
  }
  return current;
}

console.log(reduce([1, 2, 3, 4], (a, b) => a + b, 0));
// → 10

reduce

var sum = _.reduce([1, 2, 3], function(memo, num){ return memo + num; }, 0);
=> 6

javascript reduce

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.

reduce method

The reduce() method executes a reducer function (that you provide) on each element of the array, resulting in single output value.

The reducer function takes four arguments:
Accumulator (acc)
Current Value (cur)
Current Index (idx)
Source Array (src)

//syntax
arr.reduce(callback( accumulator, currentValue, [, index[, array]] )[, initialValue])
//example flatten an array

let flattened = [[0, 1], [2, 3], [4, 5]].reduce(
  ( accumulator, currentValue ) => accumulator.concat(currentValue),
  []
)

reduce in javascript

// Reduce in javascript advance
// output: { '22': 2, '24': 2, '26': 1 }
const user = [
  {name:"Abhishek",age:24},
  {name:"Dhruval",age:22},
  {name:"Anish",age:26},
  {name:"Aakash",age:22},
  {name:"Darshil",age:24},
]
const newUser = user.reduce((acc,cur)=>{
  if(acc[cur.age]){
    acc[cur.age] = acc[cur.age] +1 
  }
  else{
    acc[cur.age] = 1 
  }
  return acc;
},{})

console.log(newUser)

reduce in js

var totalYears = pilots.reduce(function (accumulator, pilot) {
  return accumulator + pilot.years;
}, 0);

reduce javascript

//note idx and sourceArray are optional
const sum = array.reduce((accumulator, element[, idx[, sourceArray]]) => {
	//arbitrary example of why idx might be needed
	return accumulator + idx * 2 + element 
}, 0);

reduce method

[0, 1, 2, 3, 4].reduce(
  (accumulateur, valeurCourante) => accumulateur + valeurCourante;
);

reduce javascript

// use of reduce on an array, returns an array into a single value

// define the array
let numbers = [25, 25, 20]

// using the .reduce() to ADD all the numbers into a single value
// we are storing the reduce method into a single variable called sum
let sum = numbers.reduce(function(total, current) {
	return total + current // adds the current value (10) and the total value (0) 
}, 0); // the }, 0) is important because we want our total value to be 0.

JavaScript Reducer

const reviews = [4.5, 4.0, 5.0, 2.0, 1.0, 5.0, 3.0, 4.0, 1.0, 5.0, 4.5, 3.0, 2.5, 2.0];
const reviewsLetter = ['c', 'd', 'f', 'a', 'g', 'a', 'd', 'f', 'e', 'b'];
// 1. Using the reduce function, create an object that// has properties for each review value, where the value// of the property is the number of reviews with that score.// for example, the answer should be shaped like this:// { 4.5: 1, 4: 2 ...}
const countGroupedByReview = reviewsLetter.reduce(groupBy, {});
function groupBy (acc, review){  
  const count = acc[review] || 0;  
  return {...acc, [review]: count + 1}}
console.log(countGroupedByReview);

Reduce use

//Array Reduce
let arr=[12,14,15,28]
let numarr=arr.reduce((h1,h2)=>{
  return h1+h2
})
console.log(numarr)

reduce javascript

let fil = res.map(x=>Object.keys(x).filter(x=>x!='process' && x!='relay_type')
  .reduce((a,b)=>{
    a[b] = x[b]
    return a
  },{})).map(x=>Object.assign(x,{total:'wew'}))

javascript reduce

let arr = [1,2,3]

/*
reduce takes in a callback function, which takes in an accumulator
and a currentValue.

accumulator = return value of the previous iteration
currentValue = current value in the array

*/

// So for example, this would return the total sum:

const totalSum = arr.reduce(function(accumulator, currentVal) {
	return accumulator + currentVal
}, 0);

> totalSum == 0 + 1 + 2 + 3 == 6

/* 
The '0' after the callback is the starting value of whatever is being 
accumulated, if omitted it will default to whatever the first value in 
the array is, i.e: 

> totalSum == 1 + 2 + 3 == 6

if the starting value was set to -1 for ex, the totalSum would be:
> totalSum == -1 + 1 + 2 + 3 == 5
*/


// arr.reduceRight does the same thing, just from right to left

Reducer

// Arrow function
reduce((accumulator, currentValue) => { ... } )
reduce((accumulator, currentValue, index) => { ... } )
reduce((accumulator, currentValue, index, array) => { ... } )
reduce((accumulator, currentValue, index, array) => { ... }, initialValue)

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

// Inline callback function
reduce(function callbackFn(accumulator, currentValue) { ... })
reduce(function callbackFn(accumulator, currentValue, index) { ... })
reduce(function callbackFn(accumulator, currentValue, index, array){ ... })
reduce(function callbackFn(accumulator, currentValue, index, array) { ... }, initialValue)

javascript reducers

// function that takes in the current state, and an action to update it 
// you just pass whatever the action you want to perform on the current state
// and it will go ahead and update it 

const arr = [2, 10, 40];
const initValue = 0;

const sumWithInitValue = arr.reduce((prevValue, currentValue) => {
  		return prevValue + currentValue 
	}, initValue);


console.log(`sum is ${sumWithInitValue}`)	// > "sum is 52"

reduce javascript

let arr = [{
name:"MAERON",
target:1,
},
{
name:"MAERON1",
target:1,
}]

let final = arr.map(x=> Object.keys(x).filter(x=> ['target'].includes(x)).reduce((a,b)=> {
a[b] = x[b]
return a
},{}))
console.log(final)

Reducer

import jwt_decode from "jwt-decode";
const initState = {
  loading: false,
  signUpErrors: [],
  loginErrors: [],
  token: "",
  user: "",
};

const verifyToken = (token) => {
  const decodeToken = jwt_decode(token);
  const expireIn = new Date(decodeToken.exp * 1000);
  if (new Date() > expireIn) {
    localStorage.removeItem("MyToken");
  } else {
    return decodeToken;
  }
};
const token = localStorage.getItem("MyToken");
if (token) {
  const decoded = verifyToken(token);
  initState.token = token;
  const { userData } = decoded;
  initState.user = userData;
}
const AuthReducer = (state = initState, action) => {
  if (action.type === "SET_LOADER") {
    return { ...state, loading: true };
  } else if (action.type === "CLOSE_LOADER") {
    return { ...state, loading: false };
  } else if (action.type === "SIGNUP_ERRORS") {
    return { ...state, signUpErrors: action.signupError };
  } else if (action.type === "SET_TOKEN") {
    const decoded = verifyToken(action.token);
    const { userData } = decoded;
    return {
      ...state,
      token: action.token,
      user: userData,
      signUpErrors: "",
      loginErrors: "",
    };
  } else if (action.type === "LOGOUT") {
    return { ...state, token: "", user: "" };
  } else if (action.type === "LOGIN_ERRORS") {
    return { ...state, loginErrors: action.loginErrors };
  } else {
    return state;
  }
};
export default AuthReducer;

reduce method

const doubledAndSummed = [1, 2, 3].reduce(function(accumulator, element){ return element * 2 + accumulator}, 0)
// => 12

js reduce

let newArray = array.reduce( (acc, element, index, originalArray) => {
    // return acc += element
}, initialValue)

reduce

const arr = [5, 7, 1, 8, 4];const sum = arr.reduce(function(accumulator, currentValue) {  return accumulator + currentValue;});// prints 25console.log(sum);