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Swift - Swift Advance functions
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  Introduction with advance functions

Let's take an scenario to understand advance function in better way,

struct User {
    var name: String
    var age: Int
    var country: String?
}

//User's information 
let user1 = User(name: "John", age: 24, country: "USA")
let user2 = User(name: "Chan", age: 20, country: nil)
let user3 = User(name: "Morgan", age: 30, country: nil)
let user4 = User(name: "Rachel", age: 20, country: "UK")
let user5 = User(name: "Katie", age: 23, country: "USA")
let user6 = User(name: "David", age: 35, country: "USA")
let user7 = User(name: "Bob",age: 22, country: nil)

//User's array list
let arrUser = [user1, user2, user3, user4, user5, user6, user7]

Map Function:

Use map to loop over a collection and apply the same operation to each element in the collection. The map function returns an array containing the results of applying a mapping or transform function to each item.

//Fetch all the user's name from array 
let arrUserName = arrUser.map({ $0.name }) // ["John", "Chan", "Morgan", "Rachel", "Katie", "David", "Bob"]

Flat-Map Function:

The simplest use is as the name suggests to flatten a collection of collections.

// Fetch all user country name & ignore nil value.
let arrCountry = arrUser.flatMap({ $0.country }) // ["USA", "UK", "USA", "USA"]

Filter Function:

Use filter to loop over a collection and return an Array containing only those elements that match an include condition.

// Filtering USA user from the array user list.
let arrUSAUsers = arrUser.filter({ $0.country == "USA" }) // [user1, user5, user6]

// User chaining methods to fetch user's name who live in USA 
let arrUserList = arrUser.filter({ $0.country == "USA" }).map({ $0.name }) // ["John", "Katie", "David"]

Reduce:

Use reduce to combine all items in a collection to create a single new value.

Swift 2.3:-

//Fetch user's total age.
let arrUserAge = arrUser.map({ $0.age }).reduce(0, combine: { $0 + $1 }) //174

//Prepare all user name string with seperated by comma 
let strUserName = arrUserName.reduce("", combine: { $0 == "" ? $1 : $0 + ", " + $1 }) // John, Chan, Morgan, Rachel, Katie, David, Bob

Swift 3:-

//Fetch user's total age.
let arrUserAge = arrUser.map({ $0.age }).reduce(0, { $0 + $1 }) //174

//Prepare all user name string with seperated by comma 
let strUserName = arrUserName.reduce("", { $0 == "" ? $1 : $0 + ", " + $1 }) // John, Chan, Morgan, Rachel, Katie, David, Bob
  Flatten multidimensional array

To flatten multidimensional array into single dimension, flatMap advance functions is used. Other use case is to neglect nil value from array & mapping values. Let's check with example:-

Suppose We have an multidimensional array of cities & we want to sorted city name list in ascending order. In that case we can use flatMap function like:-

let arrStateName = [["Alaska", "Iowa", "Missouri", "New Mexico"], ["New York", "Texas", "Washington", "Maryland"], ["New Jersey", "Virginia", "Florida", "Colorado"]]

Preparing a single dimensional list from multidimensional array,

let arrFlatStateList = arrStateName.flatMap({ $0 }) // ["Alaska", "Iowa", "Missouri", "New Mexico", "New York", "Texas", "Washington", "Maryland", "New Jersey", "Virginia", "Florida", "Colorado"]

For sorting array values, we can use chaining operation or sort flatten array. Here below example showing chaining operation,

// Swift 2.3 syntax 
let arrSortedStateList = arrStateName.flatMap({ $0 }).sort(<) // ["Alaska",     "Colorado", "Florida", "Iowa", "Maryland", "Missouri", "New Jersey", "New Mexico", "New York", "Texas", "Virginia", "Washington"]

// Swift 3 syntax
let arrSortedStateList = arrStateName.flatMap({ $0 }).sorted(by: <) // ["Alaska", "Colorado", "Florida", "Iowa", "Maryland", "Missouri", "New Jersey", "New Mexico", "New York", "Texas", "Virginia", "Washington"]



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https://develop.horje.com/learn/1434/reference

 

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