array.reduce EXAMPLES

Question 1

const numbers = [1,2,3];

ADD NUMBERS with REDUCE

console.log(x);// 6

Answer 1

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

Question 2

const numbers = [ {x:1}, {x:2}, {x:3} ];

ADD NUMBERS with REDUCE
var sum = [{x: 1}, {x: 2}, {x: 3}].reduce

console.log(x);// 6

Answer 2

var initialValue = 0;
((accumulator, currentValue)
=> accumulator + currentValue.x;
,initialValue);

console.log(sum) // logs 6

Question 3

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

Flatten array

console.log(x);// [1, 2, 3, 4];

Answer 3

numbers.reduce((a, b) a.concat(b));

Question 4

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

let x = numbers.reduce((accumulator, currentValue)=> accumulator + currentValue);

console.log(x);// returns

Answer 4

13, 4

Question 5

var names = [‘Alice’, ‘Bob’, ‘Tiff’, ‘Bruce’, ‘Alice’];

var countedNames = 
//Counting instances of values in an object

// countedNames is:
// { 'Alice': 2, 'Bob': 1, 'Tiff': 1, 'Bruce': 1 }

Answer 5

names.reduce(function (allNames, name) { 
  if (name in allNames) {
    allNames[name]++;
  }
  else {
    allNames[name] = 1;
  }
  return allNames;
}, {});

Question 6

var myArray = ['a', 'b', 'a', 'b', 'c', 'e', 'e', 'c', 'd', 'd', 'd', 'd'];
var myOrderedArray = 
//Remove duplicate items in array

console.log(myOrderedArray);

Answer 6

myArray.reduce(function (accumulator, currentValue) {
if (accumulator.indexOf(currentValue) === -1) {
accumulator.push(currentValue);
}
return accumulator
}, [])

Question 7

const numbers = [1,2,3];
numbers.reduce((accumulator, currentValue)=> accumulator + currentValue);

//WRITE OUT OLD WAY

let sum =

Answer 7

let sum = 0;
for (let n of numbers)
sum+= n;

Question 8

WHY DOES THIS RETURN AN ARRAY

const numbers = [1, 2, 3];

function sum(...arg){
console.log(arg);
return arg.reduce((a, cv) => a + cv);
};

console.log(sum([1,2,3]));

Answer 8

…arg turns an array into an array.

Question 9

const numbers = [1, 2, 3];

function sum(...arg){
// Write the If statement to check to see if arg is an array and set it to a array

return arg.reduce((a, cv) => a + cv);
};

console.log(sum([1]));

Answer 9

if (Array.isArray(arg[0]))

arg = […arg[0]];