Swift 2 - Splitting an array into a dictionary with keys A to Z
Using only Swift 2 objects and methods and with a key for each letter in the alphabet:
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)
source to share
I wrote this in the Xcode playground:
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)")
}
source to share
I found this question, helped me to better understand some of the concepts I was thinking about. Here is an alternative approach based on the accepted correct answer that is slightly more concise and where the alphabet is generated programmatically. This is Swift 2 in Xcode 7.
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)
I believe but not sure if the string let alphabet
could be more concise.
source to share
Here is my solution. Works in pure Swift 2 and in O (n) time, where n is the length of the wordlist (and assumes the dictionary is implemented as a hash table).
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)")
source to share
I just made such a useful array extension that allows you to map an array of objects to a dictionary of indexed object symbols based on a selected property of the object.
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
}
}
source to share