//
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// CollectionExtensions.swift
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// SwifterSwift
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//
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// Created by Sergey Fedortsov on 19.12.16.
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// Copyright © 2016 SwifterSwift
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//
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#if canImport(Dispatch)
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import Dispatch
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#endif
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// MARK: - Methods
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public extension Collection {
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#if canImport(Dispatch)
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/// SwifterSwift: Performs `each` closure for each element of collection in parallel.
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///
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/// array.forEachInParallel { item in
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/// print(item)
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/// }
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///
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/// - Parameter each: closure to run for each element.
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func forEachInParallel(_ each: (Self.Element) -> Void) {
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let indicesArray = Array(indices)
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DispatchQueue.concurrentPerform(iterations: indicesArray.count) { (index) in
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let elementIndex = indicesArray[index]
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each(self[elementIndex])
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}
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}
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#endif
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/// SwifterSwift: Safe protects the array from out of bounds by use of optional.
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///
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/// let arr = [1, 2, 3, 4, 5]
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/// arr[safe: 1] -> 2
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/// arr[safe: 10] -> nil
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///
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/// - Parameter index: index of element to access element.
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subscript(safe index: Index) -> Element? {
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return indices.contains(index) ? self[index] : nil
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}
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/// SwifterSwift: Returns an array of slices of length "size" from the array. If array can't be split evenly, the final slice will be the remaining elements.
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///
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/// [0, 2, 4, 7].group(by: 2) -> [[0, 2], [4, 7]]
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/// [0, 2, 4, 7, 6].group(by: 2) -> [[0, 2], [4, 7], [6]]
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///
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/// - Parameter size: The size of the slices to be returned.
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/// - Returns: grouped self.
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func group(by size: Int) -> [[Element]]? {
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// Inspired by: https://lodash.com/docs/4.17.4#chunk
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guard size > 0, !isEmpty else { return nil }
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var start = startIndex
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var slices = [[Element]]()
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while start != endIndex {
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let end = index(start, offsetBy: size, limitedBy: endIndex) ?? endIndex
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slices.append(Array(self[start..<end]))
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start = end
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}
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return slices
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}
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}
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// MARK: - Methods (Int)
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public extension Collection where Index == Int {
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/// SwifterSwift: Get all indices where condition is met.
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///
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/// [1, 7, 1, 2, 4, 1, 8].indices(where: { $0 == 1 }) -> [0, 2, 5]
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///
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/// - Parameter condition: condition to evaluate each element against.
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/// - Returns: all indices where the specified condition evaluates to true. (optional)
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func indices(where condition: (Element) throws -> Bool) rethrows -> [Index]? {
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var indicies: [Index] = []
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for (index, value) in lazy.enumerated() where try condition(value) {
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indicies.append(index)
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}
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return indicies.isEmpty ? nil : indicies
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}
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/// SwifterSwift: Calls the given closure with an array of size of the parameter slice.
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///
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/// [0, 2, 4, 7].forEach(slice: 2) { print($0) } -> // print: [0, 2], [4, 7]
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/// [0, 2, 4, 7, 6].forEach(slice: 2) { print($0) } -> // print: [0, 2], [4, 7], [6]
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///
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/// - Parameters:
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/// - slice: size of array in each interation.
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/// - body: a closure that takes an array of slice size as a parameter.
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func forEach(slice: Int, body: ([Element]) throws -> Void) rethrows {
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guard slice > 0, !isEmpty else { return }
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var value: Int = 0
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while value < count {
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try body(Array(self[Swift.max(value, startIndex)..<Swift.min(value + slice, endIndex)]))
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value += slice
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}
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}
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}
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// MARK: - Methods (Integer)
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public extension Collection where Element == IntegerLiteralType, Index == Int {
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/// SwifterSwift: Average of all elements in array.
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///
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/// - Returns: the average of the array's elements.
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func average() -> Double {
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// http://stackoverflow.com/questions/28288148/making-my-function-calculate-average-of-array-swift
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return isEmpty ? 0 : Double(reduce(0, +)) / Double(count)
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}
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}
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// MARK: - Methods (FloatingPoint)
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public extension Collection where Element: FloatingPoint {
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/// SwifterSwift: Average of all elements in array.
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///
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/// [1.2, 2.3, 4.5, 3.4, 4.5].average() = 3.18
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///
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/// - Returns: average of the array's elements.
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func average() -> Element {
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guard !isEmpty else { return 0 }
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return reduce(0, {$0 + $1}) / Element(count)
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}
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}
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