[英]Swift 2 - Separating an array into a dictionary with keys from A to Z
我有一個數組,例如["Apple", "Banana", "Blueberry", "Eggplant"]
,我想將其轉換為如下字典:
[
"A" : ["Apple"],
"B" : ["Banana", "Blueberry"],
"C" : [],
"D" : [],
"E" : ["Eggplant"]
]
我在Xcode 7 beta 4上使用Swift 2.謝謝!
僅使用Swift 2對象和方法,並使用字母表中每個字母的鍵:
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中編寫了這個:
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)")
}
我發現這個問題幫助我更好地理解了我一直在思考的一些概念。 這是基於可接受的正確答案的替代方案,該答案稍微簡潔並且以編程方式生成字母表。 這是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)
我相信但不確定let alphabet
線可以更簡潔。
這是我的解決方案。 適用於純Swift 2和O(n)時間,其中n是單詞列表的長度(假設字典是作為哈希表實現的)。
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)")
我剛剛制作了這樣有用的數組擴展,它可以根據對象的選定屬性將對象數組映射到字符索引對象字典。
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
}
}
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