Map, filter, and reduce in Swift, explained with emoji

map-filter-reduce.playground

// Map

func cook(_ item: String) -> String {
  let cookupTable = [
    "🐮": "🍔", // Cow face -> burger
    "🐄": "🍔", // Cow -> burger
    "🐂": "🍖", // Ox -> meat on bone
    "🐷": "🍖", // Pig face -> meat on bone
    "🐽": "🍖", // Pig nose -> meat on bone
    "🐖": "🍖", // Pig -> meat on bone
    "🐑": "🍖", // Sheep -> meat on bone
    "🐐": "🍖", // Goat -> meat on bone
    "🐔": "🍗", // Chicken -> poultry leg
    "🦃": "🍗", // Turkey -> poultry leg
    "🐸": "🍗", // Frog  -> poultry leg (no frog leg emoji...yet)
    "🐟": "🍣", // Fish -> sushi
    "🐠": "🍣", // Tropical fish -> sushi
    "🐡": "🍣", // Blowfish -> sushi
    "🐙": "🍣", // Octopus -> sushi
    "🍠": "🍟", // (Sweet) potato -> French fries
    "🌽": "🍿", // Corn -> popcorn
    "🌾": "🍚", // Rice -> cooked rice
    "🍓": "🍰", // Strawberry -> shortcake
    "🍂": "🍵", // Dried leaves -> tea
  ]
  if let cookedFood = cookupTable[item] {
    return cookedFood
  }
  else {
    return "🍽" // Empty plate
  }
}

let cookedFood = ["🐮", "🍠", "⚽️", "🐔", "🌽"].map { cook($0) }
cookedFood // ["🍔", "🍟", "🍽", "🍗", "🍿"]


// Filter

func isVegetarian(_ item: String) -> Bool {
  let vegetarianDishes = Set([
    "🍟", // French fries
    "🍿", // Popcorn
    "🍚", // Cooked rice
    "🍰", // Shortcake
    "🍵", // Tea
  ])
  return vegetarianDishes.contains(item)
}

let meatFree = ["🍔", "🍖", "🍟", "🍽", "🍗", "🍿", "🍰"].filter { isVegetarian($0) }
meatFree // ["🍟", "🍿", "🍰"]


// Reduce

func eat(_ previous: String, _ current: String) -> String {
  let qualifyingFood = Set([
    "🍔", // Burger
    "🍖", // Meat on bone
    "🍗", // Poultry leg
    "🍣", // Sushi
    "🍟", // French fries
    "🍿", // Popcorn
    "🍚", // Cooked rice
    "🍰", // Shortcake
  ])
  if (previous == "" || previous == "💩") && qualifyingFood.contains(current) {
    return "💩" // Poop
  }
  else {
    return ""
  }
}

let aftermath = ["🍔", "🍟", "🍗", "🍿"].reduce("", combine: eat)
aftermath // "💩"