Loop and array helper method

//string
//array loop
//array
//most used
//Most looping system
//object
//for in
//--------array convertion (array loop)

//for
//while loop
//forEach

//map
// return array
// work on each element
//don't mutate original array
//must be returned from inside

// const arrayMultiply = nums.map(num => num * 2)

// console.log(arrayMultiply)

//find
// return single element
// work on each element
//don't mutate original array
//must be returned from inside

// const result = nums.find(num => num % 2 !== 0 )
// console.log(result)

// const nums = [1, 3, 5, 7, 10]

// filter
// return array [element] based on condition
// work on each element
// don't mutate original array
// must be returned from inside
// const result = nums.filter(num => num % 2 == 0)
// console.log(result)

// const nums = [ 1,3, 5, 7]

//some
// return true/false based on condition
// work on each element
//don't mutate original array
//must be returned from inside
// const result = nums.some(num => num % 2 == 0)
// console.log(result)

//const nums = [1, 3, 5, 7]

//every
// return true/false based on condition
// work on each element
//don't mutate original array
//must be returned from inside
// const result = nums.every(num => num % 2 !== 0)
// console.log(result)

// const nums = [0, 3, 5, 7]

// findIndex
// return index number based on condition
// work on each element
// don't mutate original array
// must be returned from inside
// const result = nums.findIndex(num => num % 2 !== 0)
// console.log(result)

// reduce(reducing array element)
// return based on criteria
// work on each element
// don't mutate original array
// must be returned from inside
// const nums = [0, 3, 5, 7]

// acc - 0  curr-3 result - 3
// acc - 3  curr-5 result - 8
// acc - 8  curr-7 result - 15

// with default value
// acc - 5  curr-0 result - 5
// acc - 5  curr-3 result - 8
// acc - 8  curr-5 result - 13
// acc - 13  curr-7 result -20

// const result = nums.reduce((acc, curr, index, array) => acc + curr, 5)
// console.log(result)

// const nums = {
//   value1: 1,
//   value2: 2,
//   value3: 3
// }

// console.log(Object.keys(nums))
// console.log(Object.entries(nums))
// let total = 0
// //object looping
// for (let [key, value] of Object.entries(nums)) {
//   // total = total + value
//   //console.log(num[1])
//   // console.log(nums[num])
// }
// console.log(total)

// function summation(){
//   //for of
//   let total = 4
//   for (let num of nums){
//     total += num
//   }
//   return total

// }

//console.log(summation())

//for in(object, array-not recommended)

//array helper - map, reduce, find, findIndex, filter, some , every

// let kvArray = [{ key: 1, value: 10 },
// { key: 2, value: 20 },
// { key: 3, value: 30 }]

// let reformattedArray = kvArray.map(obj => {
//   let rObj = {}
//   rObj[obj.key] = obj.value
//   return rObj
// })
// reformattedArray is now [{1: 10}, {2: 20}, {3: 30}],

// let people = [
//   { name: 'Alice', age: 21 },
//   { name: 'Max', age: 20 },
//   { name: 'Jane', age: 20 }
// ];

// function groupBy(objectArray, property) {
//   return objectArray.reduce(function (acc, obj) {
//     let key = obj[property]
//     if (!acc[key]) {
//       acc[key] = []
//     }
//     acc[key].push(obj)
//     return acc
//   }, {})
// }

// let groupedPeople = groupBy(people, 'age')
// groupedPeople is:
// {
//   20: [
//     { name: 'Max', age: 20 },
//     { name: 'Jane', age: 20 }
//   ],
//   21: [{ name: 'Alice', age: 21 }]
// }

// let names = ['Alice', 'Bob', 'Tiff', 'Bruce', 'Alice']

// let countedNames = names.reduce(function (allNames, name) {
//   if (name in allNames) {
//     allNames[name]++
//   }
//   else {
//     allNames[name] = 1
//   }
//   return allNames
// }, {})
// countedNames is:
// { 'Alice': 2, 'Bob': 1, 'Tiff': 1, 'Bruce': 1 }

// let myArray = ['a', 'b', 'a', 'b', 'c', 'e', 'e', 'c', 'd', 'd', 'd', 'd']
// let myOrderedArray = myArray.reduce(function (accumulator, currentValue) {
//   if (accumulator.indexOf(currentValue) === -1) {
//     accumulator.push(currentValue)
//   }
//   return accumulator
// }, [])

// console.log(myOrderedArray)

//0 +1 = 1
//1 + 2 = 3
//3 + 3 = 6
// let sum = [{ x: 1 }, { x: 2 }, { x: 3 }].reduce(function (accumulator, currentValue) {
//   console.log(accumulator, currentValue)
//   return accumulator.x + currentValue.x
// })

// console.log(sum)

// let names = ['Alice', 'Bob', 'Tiff', 'Bruce', 'Alice']

// let countedNames = names.reduce(function (allNames, name) {
//   console.log(allNames, name)
//   if(allNames[name]){
//     allNames[name] ++
//   }else{
//     allNames[name] = 1
//   }
//   return allNames
// }, {})

// console.log(countedNames)

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

// const  obj = {
//   alice: 1,
//   alice: 1
// }

// console.log('alice' in obj )

let friends = [
  {
    name: 'Anna',
    books: ['Bible', 'Harry Potter'],
    age: 21
  },
  {
    name: 'Bob',
    books: ['War and peace', 'Romeo and Juliet'],
    age: 26
  },
  {
    name: 'Alice',
    books: ['The Lord of the Rings', 'The Shining'],
    age: 18
  }
]

// allbooks - list which will contain all friends' books +
// additional list contained in initialValue
let allbooks = friends.reduce(function (accumulator, currentValue) {
  console.log(accumulator, currentValue)
  return [...accumulator, ...currentValue.books]
}, [])

console.log(allbooks)