A Swift 3 example of mapValue(), a map() variant that only converts value of dictionary receiver and returns as a new dictionary instead of array.

MapValueExample.swift

//
//  MapValueExample.swift
//  ViKi
//
//  Created by Thongchai Kolyutsakul on 29/5/17.
//
//

import Foundation
import SwiftyJSON

struct MyStruct {
  let titles: [String: String] // keyed by language
  
  init(json: JSON) {
    self.titles = json["titles"].stringsDictionaryValue
  }
}

private extension JSON {
  // Converts receiver to [String: String], or empty [:] if cannot.
  var stringsDictionaryValue: [String: String] {
    return self.dictionaryValue.mapValues{ $0.stringValue }
  }
}

private extension Dictionary {
  // Maps only the values of receiver and returns as a new dictionary.
  // Note: The traditional map function returns an array.
  func mapValues<T>(_ transform: (Value)->T) -> Dictionary<Key,T> {
    var resultDict = [Key: T]()
    for (k, v) in self {
      resultDict[k] = transform(v)
    }
    return resultDict
  }
}