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Commit c94f5cd

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Bob Lee
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Finished doc for Advanced Swift
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‎course/swift4/advanced-dictionary.md‎

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# Advanced Dictionary
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## Introduction
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## Problem
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Welcome to Lesson 5, Advanced Dictionary of What's New in Swift 4. Before I say anything about this lesson. I have you warn you what would happen by the time the you will have completed this course. First, you would feel a sense of superiority, even feel over-confidence because most developers do not code the way you will. Let's find out what I mean by the previous statement.
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## Problem
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Functional programming met Swift dictionary
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### Default Value
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First, let's begin with a warm-up.
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```swift
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var myInfo = ["name": "Bob Lee", "age": "14"]
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let name = myInfo["name"] // Optional("Bob Lee")
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```
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When you attempt to access a value, the dictionary return an optional type. In Swift 4, however, you may prevent that from happening.
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```swift
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let footSize = myInfo["footsize", default: "No Value"] // "No Value"
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let myName = myInfo["name", default: "No Value"] // "Name"
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let footSize = myInfo["footsize", default: "No Value"] // "No Value"
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```
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> I'd use it everywhere.
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> I'd use it everywhere since I do not like optionals floating around in my codebase. Optional types represent death for other lines of code. To prevent death, you have to add more lines of code.
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### Grouping a sequence into a dictionary
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The `Dictionary` struct provides a couple custom initializers that allow you to create a dictionary using an array.
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```swift
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let contacts = ["Julia", "Susan", "John", "Alice", "Alex"]
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let grouped = Dictionary(grouping: contacts, by: { 0ドル.first! })
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grouped // ["J": ["Julia", "John"], "S": ["Susan"], "A": ["Alice", "Alex"]]
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```
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I don't exactly know the custom init method looks like. As the parameter indicates, it requires the value of each element in the array.
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### Unique Key
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You may also create an array filled with tuple to a dictionary with unique keys.
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```swift
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let duplicates = [("a", 1), ("b", 7), ("a", 3), ("b", 4)]
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let myLetter = Dictionary(duplicates, uniquingKeysWith: { (first, _) in first })
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let myLetter = Dictionary(duplicates, uniquingKeysWith: { (letter, number) in letter })
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uniquingKeysWith // ["b": 7, "a": 1]
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```
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What a powerful way to manipulate an array of tuples.
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### Zip (Dictionary Like)
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Some may not be familiar with `Zip`. Let's go over before moving on to the next step.
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```swift
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let words = ["one", "two", "three", "four"]
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let numbers = 1...4
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let numbers = 1...words.count
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for (word, number) in zip(words, numbers) {
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print("\(word): \(number)")
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// Prints "four: 4"
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```
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Zip to Dictionary
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For `zip`, the parameters must conform to the `sequence` protoocol. You will learn more about it in the next chapter.
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### Zip to Dictionary
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Let us apply `Zip` to create a beautiful dictionary.
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```swift
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let friends = ["Hoy", "Dan", "Huy"]
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let friendsWithValue = Dictionary(uniqueKeysWithValues: zip(1..., friends))
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```
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> You don't need to memorize. All you need to know is, "things" exist.
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### Functional Programming with Set
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In the past, when you apply built-in functions such as `filter`, it returns `Array<T>`. In Swift, it returns `Set<T>`
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```swift
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let set: Set = [1,2,3,4,5]
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let filteredSet = set.filter { 0ドル % 2 == 0 } // Returns Set
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type(of: filteredSet)
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type(of: filteredSet)// Set
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```
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### Functional Programming with Dictionary
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Now, this is the real deal. You will never the code the same way if you understand this. But, again, this should be a review of the previous chapters.
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```
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```swift
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let dictionary = ["name": "Bob", "age": "15", "hairColor": "Black"]
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let filtered = dictionary.filter {
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0ドル.key == "name"
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}
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print(filtered)
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print(filtered) // ["name": "Bob"]
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```
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This is just purely beautiful and nice.
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```swift
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let mapped = dictionary.mapValues { value in
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value.uppercased()
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}
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print(mapped)
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print(mapped)// ["name": "BOB", "age": "15", "hairColor": "BLACK"]
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```
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This is just short and nice. Amazing code. I love it.
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## Conclusion
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That's it. That's just it. As I promised, you will never code the way you've been doing in the past. In fact, Swift 4 has changed my perspectives towards how to manipulate key-value in Dictionary. But, still, some may feel overwhelmed by the amount of information that I've presented to you thus far. Don't you worry. I do not want you to memorize. In fact, memorization isn't needed anymore in this world where the internet and your left hand, Google is available 24/7. As I mentioned, all you need to know is, "I've been it before and those things exist". That's it. All you have to do is search and learn more!
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Do not try to memorize any, simply understand the fundamentals and look at API guidelines and references for your usage. At least it works out for me.
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### Source Code
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[9005_advanced_dictionary.playground]()

‎source-code/9000_swift4/.DS_Store‎

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‎source-code/9000_swift4/9005_advanced_dictionary.playground/Pages/8001_nested_generics_recursive_enum.xcplaygroundpage/Contents.swift‎

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print(grouped)
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let duplicates = [("a", 1), ("b", 7), ("a", 3), ("b", 4)]
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let myLetter = Dictionary(duplicates, uniquingKeysWith: { (first, _) in first })
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let duplicates = [("a", 1), ("b", 7), ("a", 3), ("b", 10)]
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let myLetter = Dictionary(duplicates, uniquingKeysWith: { (letter, number) in letter })
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print(myLetter)
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//: ### Zip: (Dictionary Like)
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let words = ["one", "two", "three", "four"]
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let numbers = 1...4
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let numbers = 1...words.count
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for (word, number) in zip(words, numbers) {
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print("\(word): \(number)")
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<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
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<playground version='6.0' target-platform='ios' display-mode='raw'/>
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<playground version='6.0' target-platform='ios' display-mode='rendered'/>

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