{"id":2712,"date":"2026-02-05T11:09:16","date_gmt":"2026-02-05T11:09:16","guid":{"rendered":"https:\/\/demo.materiamedica.net\/demo6\/?p=2712"},"modified":"2026-02-05T11:09:16","modified_gmt":"2026-02-05T11:09:16","slug":"chapter-63-swift-collections","status":"publish","type":"post","link":"https:\/\/demo.materiamedica.net\/demo6\/chapter-63-swift-collections\/","title":{"rendered":"Chapter 63: Swift Collections"},"content":{"rendered":"

The Big Picture: What are Collections and Why Three Main Types?<\/h3>\n

A collection<\/strong> in Swift is any type that holds zero or more values<\/strong>.<\/p>\n

Swift gives you three main choices<\/strong> for everyday work \u2014 each solves a different problem:<\/p>\n

\n
\n\n\n\n\n\n\n\n
Collection Type<\/th>\nOrdered?<\/th>\nAllows duplicates?<\/th>\nFast lookup by value?<\/th>\nFast lookup by key?<\/th>\nMost common real-life feeling<\/th>\nTypical use case examples<\/th>\n<\/tr>\n<\/thead>\n
Array<\/strong><\/td>\nYes<\/td>\nYes<\/td>\nNo (slow)<\/td>\nNo<\/td>\n\u201cI have a list of things in a specific order\u201d<\/td>\nshopping cart, to-do list, recent searches, messages<\/td>\n<\/tr>\n
Set<\/strong><\/td>\nNo<\/td>\nNo<\/strong><\/td>\nYes (very fast)<\/td>\nNo<\/td>\n\u201cI have a group of unique items \u2014 order doesn\u2019t matter\u201d<\/td>\ntags, permissions, unique IDs, friends list (no duplicates)<\/td>\n<\/tr>\n
Dictionary<\/strong><\/td>\nNo (insertion order since Swift 4.2)<\/td>\nYes (different keys)<\/td>\nNo<\/td>\nYes (very fast)<\/td>\n\u201cI have items and I want to find them by a key\/label\u201d<\/td>\nuser profile, JSON data, settings, lookup tables<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
<\/div>\n<\/div>\n<\/div>\n

Golden rule you should burn into your mind:<\/strong><\/p>\n

\n
    \n
  • Need order<\/strong> or duplicates<\/strong> \u2192 almost always Array<\/strong><\/li>\n
  • Need uniqueness<\/strong> and fast \u201cdoes it contain X?\u201d<\/strong> \u2192 Set<\/strong><\/li>\n
  • Need fast lookup by key<\/strong> (\u201cgive me value for this name\/ID\u201d) \u2192 Dictionary<\/strong><\/li>\n<\/ul>\n<\/blockquote>\n

    Chapter 2 \u2013 Arrays (the most common collection \u2013 you will use this 70\u201380% of the time)<\/h3>\n

    2.1 Creating & basic operations<\/h4>\n
    \n
    \n
    \n
    Swift<\/div>\n
    \n
    \/\/ Most common ways\r\nlet colors: [String] = [\"Red\", \"Green\", \"Blue\"]          \/\/ type annotation optional\r\nvar shoppingCart = [String]()                           \/\/ empty mutable array\r\n\r\n\/\/ Add items\r\nshoppingCart.append(\"Milk\")\r\nshoppingCart.append(contentsOf: [\"Bread\", \"Eggs\"])\r\n\r\n\/\/ Insert at specific position\r\nshoppingCart.insert(\"Butter\", at: 1)\r\n\r\n\/\/ Replace\r\nshoppingCart[0] = \"Almond Milk\"\r\n\r\n\/\/ Remove\r\nshoppingCart.remove(at: 2)           \/\/ removes \"Eggs\"\r\nlet lastItem = shoppingCart.removeLast()\r\n\r\n\/\/ Count & empty check\r\nprint(shoppingCart.count)            \/\/ 2\r\nprint(shoppingCart.isEmpty)          \/\/ false\r\n\r\n\/\/ Safe first\/last\r\nlet first = shoppingCart.first ?? \"No items\"<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
    2.2 Real-life example \u2013 shopping cart \/ order summary<\/h4>\n
    \n
    \n
    \n
    Swift<\/div>\n
    \n
    struct CartItem {\r\n    let name: String\r\n    let price: Double\r\n    let quantity: Int\r\n}\r\n\r\nvar cart: [CartItem] = []\r\n\r\ncart.append(CartItem(name: \"Wireless Earbuds\", price: 3499, quantity: 1))\r\ncart.append(CartItem(name: \"Phone Case\",       price: 799,  quantity: 2))\r\ncart.append(CartItem(name: \"Screen Protector\", price: 499,  quantity: 1))\r\n\r\nprint(\"Your Cart (\\(cart.count) items)\")\r\nprint(\"\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\u2500\")\r\n\r\nvar total: Double = 0\r\n\r\nfor (index, item) in cart.enumerated() {\r\n    let lineTotal = item.price * Double(item.quantity)\r\n    total += lineTotal\r\n    \r\n    print(\"\\(index + 1). \\(item.name) \u00d7 \\(item.quantity)\")\r\n    print(\"   \u20b9\\(String(format: \"%.2f\", item.price)) each \u2192 \u20b9\\(String(format: \"%.2f\", lineTotal))\")\r\n    print(\"\u2500\u2500\")\r\n}\r\n\r\nprint(\"Grand Total: \u20b9\\(String(format: \"%.2f\", total))\")<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
    Chapter 3 \u2013 Sets (when uniqueness matters)<\/h3>\n
    3.1 Creating & basic operations<\/h4>\n
    \n
    \n
    \n
    Swift<\/div>\n
    \n
    var tags = Set<String>()\r\n\r\ntags.insert(\"Swift\")\r\ntags.insert(\"iOS\")\r\ntags.insert(\"Beginner\")\r\ntags.insert(\"Swift\")        \/\/ duplicate \u2013 ignored\r\n\r\nprint(tags)                 \/\/ Set([\"Swift\", \"iOS\", \"Beginner\"])\r\n\r\nprint(tags.contains(\"Swift\"))     \/\/ true\r\nprint(tags.contains(\"Python\"))    \/\/ false\r\n\r\n\/\/ Add multiple\r\ntags.formUnion([\"Apple\", \"Xcode\"])\r\n\r\n\/\/ Remove\r\ntags.remove(\"Beginner\")\r\n\r\n\/\/ Count\r\nprint(tags.count)           \/\/ 5<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
    Real-life example \u2013 unique permissions \/ roles<\/strong><\/p>\n
    \n
    \n
    \n
    Swift<\/div>\n
    \n
    var userPermissions = Set<String>()\r\n\r\nuserPermissions.insert(\"read\")\r\nuserPermissions.insert(\"write\")\r\nuserPermissions.insert(\"delete\")\r\nuserPermissions.insert(\"read\")     \/\/ ignored\r\n\r\nif userPermissions.contains(\"delete\") {\r\n    print(\"User can delete content\")\r\n}\r\n\r\nif userPermissions.isSuperset(of: [\"read\", \"write\"]) {\r\n    print(\"User has read & write access\")\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
    Chapter 4 \u2013 Dictionaries (lookup by key)<\/h3>\n
    4.1 Creating & basic operations<\/h4>\n
    \n
    \n
    \n
    Swift<\/div>\n
    \n
    var profile: [String: Any] = [\r\n    \"name\": \"Rahul Verma\",\r\n    \"age\": 27,\r\n    \"city\": \"Bengaluru\",\r\n    \"isPremium\": true,\r\n    \"points\": 14520\r\n]\r\n\r\n\/\/ Access\r\nif let name = profile[\"name\"] as? String {\r\n    print(\"Name: \\(name)\")\r\n}\r\n\r\n\/\/ Update\r\nprofile[\"points\"] = 15000\r\n\r\n\/\/ Add new\r\nprofile[\"favoriteColor\"] = \"Blue\"\r\n\r\n\/\/ Remove\r\nprofile[\"age\"] = nil\r\n\r\n\/\/ Loop\r\nfor (key, value) in profile {\r\n    print(\"\\(key): \\(value)\")\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
    Real-life example \u2013 user profile \/ settings<\/strong><\/p>\n
    \n
    \n
    \n
    Swift<\/div>\n
    \n
    var userSettings: [String: Any] = [\r\n    \"darkMode\": true,\r\n    \"notificationsEnabled\": true,\r\n    \"fontSize\": 16,\r\n    \"language\": \"en\",\r\n    \"locationSharing\": false\r\n]\r\n\r\n\/\/ Apply settings\r\nif let darkMode = userSettings[\"darkMode\"] as? Bool, darkMode {\r\n    applyDarkTheme()\r\n}\r\n\r\nif let fontSize = userSettings[\"fontSize\"] as? CGFloat {\r\n    setFontSize(fontSize)\r\n}<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
    Modern style (strongly typed dictionary)<\/strong><\/p>\n
    \n
    \n
    \n
    Swift<\/div>\n
    \n
    enum SettingKey: String {\r\n    case darkMode\r\n    case notificationsEnabled\r\n    case fontSize\r\n    case language\r\n}\r\n\r\nvar typedSettings: [SettingKey: Any] = [\r\n    .darkMode: true,\r\n    .fontSize: 16\r\n]<\/code><\/pre>\n<\/div>\n<\/div>\n<\/div>\n<\/div>\n
    Chapter 5 \u2013 Quick Comparison Table (keep this in mind)<\/h3>\n
    \n
    \n\n\n\n\n\n\n\n
    You want to…<\/th>\nUse this collection<\/th>\nTypical operations<\/th>\nExample real-life case<\/th>\n<\/tr>\n<\/thead>\n
    Keep order, allow duplicates<\/td>\nArray<\/td>\nappend, insert(at:), remove(at:), enumerated()<\/td>\nshopping cart, task list, chat messages<\/td>\n<\/tr>\n
    Ensure uniqueness, fast \u201ccontains?\u201d<\/td>\nSet<\/td>\ninsert, contains, remove, union\/intersection<\/td>\ntags, permissions, unique IDs, friends (no dupes)<\/td>\n<\/tr>\n
    Fast lookup by key<\/td>\nDictionary<\/td>\n[key] = value, updateValue(forKey:), removeValue<\/td>\nuser profile, settings, JSON data, lookup tables<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n
    <\/div>\n<\/div>\n<\/div>\n
    Chapter 6 \u2013 Small Practice \u2013 Try these<\/h3>\n
      \n
    1. Create an array<\/strong> of 5 favorite foods \u2192 Print them numbered \u2192 Add one more at the beginning \u2192 Remove the last one<\/li>\n
    2. Create a set<\/strong> of 6 tags (some duplicates) \u2192 Add 2 more \u2192 Check if “Swift” is present \u2192 Print all unique tags<\/li>\n
    3. Create a dictionary<\/strong> for a user profile \u2192 name, age, city, isPremium \u2192 Print all key-value pairs \u2192 Change age and add favoriteColor<\/li>\n<\/ol>\n
      Paste your code here if you want feedback or want to see more polished versions!<\/p>\n
      What would you like to explore next?<\/p>\n
        \n
      • Array<\/strong> slicing & memory behavior with slices<\/li>\n
      • Sorting<\/strong> arrays (simple & custom comparators)<\/li>\n
      • Filtering<\/strong>, mapping<\/strong>, reducing<\/strong> in depth<\/li>\n
      • Dictionaries<\/strong> in more depth (typed keys, default values)<\/li>\n
      • Sets<\/strong> operations (union, intersection, difference)<\/li>\n
      • Or move to another topic (optionals, switch, functions\u2026)<\/li>\n<\/ul>\n
        Just tell me \u2014 we\u2019ll continue in the same clear, patient, detailed style \ud83d\ude0a<\/p>\n","protected":false},"excerpt":{"rendered":"
        The Big Picture: What are Collections and Why Three Main Types? A collection in Swift is any type that holds zero or more values. Swift gives you three main choices for everyday work \u2014...<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[76],"tags":[],"class_list":["post-2712","post","type-post","status-publish","format-standard","hentry","category-swift"],"_links":{"self":[{"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/posts\/2712","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/comments?post=2712"}],"version-history":[{"count":1,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/posts\/2712\/revisions"}],"predecessor-version":[{"id":2713,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/posts\/2712\/revisions\/2713"}],"wp:attachment":[{"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/media?parent=2712"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/categories?post=2712"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/demo.materiamedica.net\/demo6\/wp-json\/wp\/v2\/tags?post=2712"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}