Swift 2 – 使用从A到Z的键将数组分离到字典中
我有一个数组，例如["Apple", "Banana", "Blueberry", "Eggplant"] ，我想将其转换为如下字典：
[ "A" : ["Apple"], "B" : ["Banana", "Blueberry"], "C" : [], "D" : [], "E" : ["Eggplant"] ]
我在Xcode 7 beta 4上使用Swift 2.谢谢！
仅使用Swift 2对象和方法，并使用字母表中每个字母的键：
let alphabet = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".characters.map({ String($0) }) let words = ["Apple", "Banana", "Blueberry", "Eggplant"] var result = [String:[String]]() for letter in alphabet { result[letter] = [] let matches = words.filter({ $0.hasPrefix(letter) }) if !matches.isEmpty { for word in matches { result[letter]?.append(word) } } } print(result)
我在Xcode playground中编写了这个：
import Foundation var myArray = ["Apple", "Banana", "Blueberry", "Eggplant"] var myDictionary : NSMutableDictionary = NSMutableDictionary() for eachString in myArray as [NSString] { let firstCharacter = eachString.substringToIndex(1) var arrayForCharacter = myDictionary.objectForKey(firstCharacter) as? NSMutableArray if arrayForCharacter == nil { arrayForCharacter = NSMutableArray() myDictionary.setObject(arrayForCharacter!, forKey: firstCharacter) } arrayForCharacter!.addObject(eachString) } for eachCharacter in myDictionary.allKeys { var arrayForCharacter = myDictionary.objectForKey(eachCharacter) as! NSArray print("for character \(eachCharacter) the array is \(arrayForCharacter)") }
我发现这个问题帮助我更好地理解了我一直在思考的一些概念。 这是基于可接受的正确答案的替代方案，该答案稍微简洁并且以编程方式生成字母表。 这是Xcode 7中的Swift 2。
let words = ["Apple", "Banana", "Blueberry", "Eggplant"] let alphabet = (0..<26).map {n in String(UnicodeScalar("A".unicodeScalars["A".unicodeScalars.startIndex].value + n))} var results = [String:[String]]() for letter in alphabet { results[letter] = words.filter({$0.hasPrefix(letter)}) } print(results)
我相信但不确定let alphabet线可以更简洁。
这是我的解决方案。 适用于纯Swift 2和O（n）时间，其中n是单词列表的长度（假设字典是作为哈希表实现的）。
var dictionary: [String : [String]] = [ "A" : [], "B" : [], "C" : [], "D" : [], "E" : [], "F" : [] /* etc */ ] let words = ["Apple", "Banana", "Blueberry", "Eggplant"] for word in words { let firstLetter = String(word[word.startIndex]).uppercaseString if let list = dictionary[firstLetter] { dictionary[firstLetter] = list + [word] } else { print("I'm sorry I can't do that Dave, with \(word)") } } print("\(dictionary)")
我刚刚制作了这样有用的数组扩展，它可以根据对象的选定属性将对象数组映射到字符索引对象的字典。
extension Array { func toIndexedDictionary(by selector: (Element) -> String) -> [Character : [Element]] { var dictionary: [Character : [Element]] = [:] for element in self { let selector = selector(element) guard let firstCharacter = selector.firstCharacter else { continue } if let list = dictionary[firstCharacter] { dictionary[firstCharacter] = list + [element] } else { // create list for new character dictionary[firstCharacter] = [element] } } return dictionary } } extension String { var firstCharacter : Character? { if count > 0 { return self[startIndex] } return nil } }