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iOS Swift 2.0 Collections and Control Flow Control Flow With Conditional Statements Working with Switch Statements

William Hartvedt Skogstad
William Hartvedt Skogstad
5,857 Points
Posted by William Hartvedt Skogstad
William Hartvedt Skogstad
5,857 Points

Here we have a dictionary of type [String: String] that contains a three letter country code as a

Challenge Task 1 of 1

Here we have a dictionary of type [String: String] that contains a three letter country code as a key and that country's capital city as the associated value.

We also have three empty arrays, europeanCapitals, asianCapitals, and otherCapitals. The goal is to iterate through the dictionary and end up with just the names of the capital cities in the relevant array.

For example, after you execute the code you write, europeanCapitals will have the values ["Vaduz", "Brussels", "Sofia"] (not necessarily in that order).

To do this you're going to use a switch statement and switch on the key. For cases where the key is a European country, append the value (not the key!) to the europeanCapitals array. For keys that are Asian countries, append the value to asianCapitals and finally for the default case, append the values to otherCapitals.

I've already set up the for in loop for you so jump right in!

switch.swift 
var europeanCapitals: [String] = []
var asianCapitals: [String] = []
var otherCapitals: [String] = []

let world = [
  "BEL": "Brussels", 
  "LIE": "Vaduz", 
  "BGR": "Sofia", 
  "USA": "Washington D.C.", 
  "MEX": "Mexico City", 
  "BRA": "Brasilia", 
  "IND": "New Delhi", 
  "VNM": "Hanoi"]

for (key, value) in world {
    // Enter your code below

    // End code
}

3 Answers

Sam Chaudry
Sam Chaudry
25,519 Points
Sam Chaudry
Sam Chaudry
25,519 Points

Hi William

I've just run this in a playground here's what you are after

var europeanCapitals: [String] = [] var asianCapitals: [String] = [] var otherCapitals: [String] = []

let world = [ "BEL": "Brussels", "LIE": "Vaduz", "BGR": "Sofia", "USA": "Washington D.C.", "MEX": "Mexico City", "BRA": "Brasilia", "IND": "New Delhi", "VNM": "Hanoi"]

for (key, value) in world {

switch key {

case "BEL", "BGR","LIE" :

    europeanCapitals.append(value)

case "IND","VNM":

    asianCapitals.append(value)

default:

    otherCapitals.append(value)

}

}

You are switching on the keys and they are the conditions that you are testing against. So create you 3 cases one European, one Asian, one Other (This your default). Then all you are doing is seeing if this case exists and if it does then run append it to the array.

The first case is

["Vaduz", "Brussels", "Sofia"]

The second case is

["Hanoi", "New Delhi"]

The default/other is:

["Mexico City", "Brasilia", "Washington D.C."]

William Hartvedt Skogstad
William Hartvedt Skogstad
5,857 Points
William Hartvedt Skogstad
William Hartvedt Skogstad
5,857 Points

Aha! A switch statement INSIDE a for in loop was the answer! thanks a lot :)

Michael Dussie
Michael Dussie
1,891 Points
Michael Dussie
Michael Dussie
1,891 Points 
var europeanCapitals: [String] = []
var asianCapitals: [String] = []
var otherCapitals: [String] = []

let world = [
  "BEL": "Brussels", 
  "LIE": "Vaduz", 
  "BGR": "Sofia", 
  "USA": "Washington D.C.", 
  "MEX": "Mexico City", 
  "BRA": "Brasilia", 
  "IND": "New Delhi", 
  "VNM": "Hanoi"]

for (key, value) in world {
    // Enter your code below
    switch key {
      case "BEL", "LIE", "BGR": 
      europeanCapitals.append(value)
      case "IND", "VNM": 
      asianCapitals.append(value)
    default: otherCapitals.append(value)
    }
    // End code
}
Kathleen Hang
Kathleen Hang
4,062 Points
Kathleen Hang
Kathleen Hang
4,062 Points

This portion of the swift documentation helped me understand why we append (value). (value) contains the capital names we want to insert into our empty arrays. Just understanding what a dictionary is and how its syntax differs from an array helped me comprehend this.

You can also iterate over a dictionary to access its key-value pairs. Each item in the dictionary is returned as a (key, value) tuple when the dictionary is iterated, and you can decompose the (key, value) tuple’s members as explicitly named constants for use within the body of the for-in loop. Here, the dictionary’s keys are decomposed into a constant called animalName, and the dictionary’s values are decomposed into a constant called legCount.

let numberOfLegs = ["spider": 8, "ant": 6, "cat": 4]
for (animalName, legCount) in numberOfLegs {
    print("\(animalName)s have \(legCount) legs")
}
// ants have 6 legs
// spiders have 8 legs
// cats have 4 legs