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Commit f787e49

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author
Bob Lee
committed
Finished Reduce
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‎course/functional-programming/reduce.md‎

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# Reduce
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## Introduction
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Welcome to Lesson 3 of Functional Programming. I don't think I have to talk too much. Let's get into the lesson right away.
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## Problem
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Combine all into one
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let subtracted = Array(1...10).reduce(0) { 0ドル - 1ドル } // -55
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```
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You will discover how it works behind the scene by the end of this lesson. Let's get started.
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You will discover how the `reduce` function works behind the scene by the end of this lesson. Let's get started.
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```swift
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func myReduce(_ seed: Int, numbers: [Int], operation: (Int, Int) -> Int) {
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var current = seed
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for number in numbers {
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current = operation(current, number)
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}
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}
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```
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`seed` represents the initial value you wish to start off with.
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### Source Code
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```swift
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myReduce(0, numbers: Array(1...10)) { 0ドル + 1ドル }
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```
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### Ex) Finding the Max
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```swift
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let maxNumber = Array(1...10).reduce(0) { (total, number) in max(total, number) }
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let bigNumber = Array(1...10).reduce(0) { max(0ドル, 1ドル) }
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```
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So far, `myReduce` has not returned any. Let's create a function that returns the final value in `Int`.
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```swift
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func reduce(_ seed: Int, numbers: [Int], operation: (Int, Int) -> Int) -> Int {
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var current = seed
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for number in numbers {
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current = operation(current, number)
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}
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return current
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}
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reduce(0, numbers: Array(1...10)) { 0ドル + 1ドル }
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```
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### Generic Reduce
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Again, creating a generic function is just a required for the sake of time and efficiency.
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### Resources
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```swift
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extension Array {
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func myReduce<U>(_ seed: U, operation:(U, U) -> U) -> U {
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var current = seed
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for item in self {
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current = operation(current, item as! U)
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}
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return current
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}
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}
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```
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Currently, there is a force casting using `as! U`. It occurs since the type of `U` is not defined until you use the `myReduce` function.
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```swift
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let names = ["Bob", "Bobby", "Lee"]
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let description = names.myReduce("Names:") { "\(0ドル) " + 1ドル }
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print(description) // "Names: Bob Bobby Lee"
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```
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Not only that, you may "chain" multiple functions.
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```swift
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let lowerNames = names.map { 0ドル.lowercased() }.myReduce("Names:") { "\(0ドル) " + 1ドル }
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print(lowerNames) // "Names: bob bobby lee"
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```
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### The Purest Form
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```swift
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//: The Purest Form
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extension Array {
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func reduce(_ seed: Element, operation:(Element, Element) -> Element) -> Element {
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var current = seed
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for item in self {
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current = operation(current, item)
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}
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return current
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}
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}
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let hello = ["Bob", "Bobby", "Lee"].reduce("Names:") { "\(0ドル) " + 1ドル }
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```
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### Source Code
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[6004_reduce.playground]()
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## Conclusion
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I hope by now you are truly seeing the power of functions. Well, a functional paradigm is not specifically tied to iOS development. In fact, you've learned how to apply and utilize closure and generics in web development, server development, Android development, and other platforms. This course isn't just about learning Swift. It is about to learn how to code with beauty and class. Let's get to the final function of this chapter.
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‎source-code/6000_functional_programming/6004_reduce.playground/Contents.swift‎

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/*:
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## Learn Swift with Bob
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### Functional Programming
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### Reduce
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### 6004_Reduce
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**Problem:** Combine all into one
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//: Let's Find Out
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func myReduce(seed: Int, numbers: [Int], operation: (Int, Int) -> Int) {
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func myReduce(_ seed: Int, numbers: [Int], operation: (Int, Int) -> Int) {
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var current = seed
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for number in numbers {
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current = operation(current, number)
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}
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}
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myReduce(seed:0, numbers: Array(1...10)) { 0ドル + 1ドル }
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myReduce(0, numbers: Array(1...10)) { 0ドル + 1ドル }
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//: Max Number
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let maxNumber = Array(1...10).reduce(0) { (total, number) in max(total, number) }
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let bigNumber = Array(1...10).reduce(0) { max(0ドル, 1ドル) }
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let maxNumber = Array(1...10).myReduce(0) { (total, number) in max(total, number) }
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let bigNumber = Array(1...10).myReduce(0) { max(0ドル, 1ドル) }
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//: Create Function that Returns
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func reduce(seed: Int, numbers: [Int], operation: (Int, Int) -> Int) -> Int {
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func reduce(_ seed: Int, numbers: [Int], operation: (Int, Int) -> Int) -> Int {
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var current = seed
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for number in numbers {
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current = operation(current, number)
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}
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return current
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}
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reduce(seed:0, numbers: Array(1...10)) { 0ドル + 1ドル }
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reduce(0, numbers: Array(1...10)) { 0ドル + 1ドル }
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//: Generic Reduce
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extension Array {
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func myReduce<U>(seed: U, operation:(U, U) -> U) -> U {
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func myReduce<U>(_ seed: U, operation:(U, U) -> U) -> U {
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var current = seed
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for item in self {
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current = operation(current, item as! U)
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}
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}
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//: Example
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let names = ["Bob", "Bobby", "Lee"]
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let description = names.myReduce(seed:"Names:") { "\(0ドル)" + 1ドル }
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let description = names.myReduce("Names:") { "\(0ドル)" + 1ドル }
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print(description)
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//: Example
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let lowerNames = names.map { 0ドル.lowercased() }.myReduce(seed:"Names:") { "\(0ドル)" + 1ドル }
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//: Multiple Functions
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let lowerNames = names.map { 0ドル.lowercased() }.myReduce("Names:") { "\(0ドル)" + 1ドル }
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print(lowerNames)
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//: The Purest Form
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extension Array {
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func reduce(seed: Element, operation:(Element, Element) -> Element) -> Element {
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func reduce(_ seed: Element, operation:(Element, Element) -> Element) -> Element {
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var current = seed
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for item in self {
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current = operation(current, item)
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}
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}
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let hello = ["Bob", "Bobby", "Lee"].reduce(seed:"Names:") { "\(0ドル)" + 1ドル }
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let hello = ["Bob", "Bobby", "Lee"].reduce("Names:") { "\(0ドル)" + 1ドル }
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