在Swift 2.2中按第二个字母对数组排序

Question

I want to sort the array by second letter of word. Some one has an idea? i will type a value and key, should return sorted list like this: array ["hello", "bye", "how", etc"] Sorted: hello, how, etc, bye

static func sort(keyValue: [(key:String, value:String)]) -> [(key:String, value:String)] {

    let returnValue = keyValue( {$0 < $1}

    return returnValue
}

Answer 1

You can use substringFromIndex with the standard sort or sortInPlace functions:

let strings = ["hello", "bye", "how", "etc"]
let sortedStrings = strings.sort { $0.substringFromIndex($0.startIndex.advancedBy(1)) < $1.substringFromIndex($1.startIndex.advancedBy(1)) }

Answer 2

As an alternative to using subStringFromIndex —an alternative suitable specifically for the case of sorting by the second character (and in case of equality; following characters lexicographically) of each string—you can use the dropFirst() method of the CharacterView of each string:

let strings = ["hello", "bye", "how", "etc"]
let sortedStrings = strings
    .sort { String($0.characters.dropFirst()) < String($1.characters.dropFirst()) }

print(sortedStrings) // ["hello", "how", "etc", "bye"]

This is equivalent to the solution using substringFromIndex and advancedBy , with the upside that this will not yield a runtime exception in case the strings array contain an empty string ( "" ) (although this can be remedied for the advancedBy solution by using .advancedBy(1, limit: $0.endIndex) and .advancedBy(1, limit: $1.endIndex) for the sorting keys, respectively).

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Note also that lexicographical comparison will sort uppercase letters prior to any lowercase letter, such that ["hello", "bYe", "hOw", "etc"] will sort into ["hOw", "bYe", "hello", "etc"] . If you want case-insensitive sorting, you can apply the .lowercaseString property to the sorting keys:

let strings = ["hello", "bYe", "hOw", "etc"]
let sortedStrings = strings
    .sort { String($0.lowercaseString.characters.dropFirst()) <
        String($1.lowercaseString.characters.dropFirst()) }

print(sortedStrings) // ["hello", "hOw", "etc", "bYe"]