(iOS) Collection higher order functions

0.map.swift

//Map
//Loops over a collection and applies the same operation to each element in the collection.

var numberArray = [1,2,3,4,5]

var newArray = numberArray.map( {(value:Int) -> Int in
  return value*2
})

//or quicker
var newArray = numberArray.map{$0*2}

//newArray = [2,4,6,8,10]

1.filter.swift

//FILTER
//Loops over a collection and returns an array that contains elements that meet a condition.

let numbersArray = [1,2,3,4,5,6,7,8,9,10,11,14,15]

//filter them
let evenArray = numbersArray.filter{$0 % 2 == 0}

2.reduce.swift

//Reduce
//Combines all items in a collection to create a single value.

var oneTwoFive = [1,2,3,4,5]

//Reduce
//The addition of two adjacent values is taking place between the {} brackets, and the sum is then added to the 0 on the left.
var sum = oneTwoFive.reduce(0, {$0 + $1})
//sum = 15

//Easier way
//the + operator is substituted for the {$0 + $1} closure, creating an even more simplified and accessible syntax
var sum = oneTwoFive.reduce(0, +)

3.flatmap.swift

//Flatmap
//When implemented on sequences : Flattens a collection of collections.

let arrayInArray = [[11,12,13],[14,15,16]]

let flattenedArray = arrayInArray.flatMap{$0}
//flattenedArray = [11,12,13,14,15,16]


//Removing nils from a collection
let people:[String?] = ["Joyce",nil,"rob",nil,"Maria"]

let validPeople = people.flatMap{$0}