how to map elements of an array with their occurrence number

Using Swift
,
#1

Hello,

I have an array of objects that has a type attribute of enum Animals. the type can be like this [Cat, Dog, Cat, Cat, Dog, Mouse, Dog]

I would like to display to my view an output of an image for every object along with the type and its number.

My problem is I cannot get the number from the array. The output should look like :

[Cat1, Dog1, Cat2, Cat3, Dog2, Mouse1, Dog3]

Any ideas how can i achieve this?

#2

Where do the numbers come from? Are they associated values of the enum cases? Are they simply generated sequentially from the order in the array?

#3

You could build up a new array, keeping track of the counts in a dictionary as you go:

var runningTotals: [Animal: Int] = [:]

var animalCounts: [Int] = []
animalCounts.reserveCapacity(animals.count)

for animal in animals {
  let n = runningTotals[animal, default: 0] + 1
  runningTotals[animal] = n
  animalCounts.append(n)
}
2 Likes
#4

The dictionary solution is good. But there are iterators built into the standard library which implement the behavior already. I think this might be the simplest one?

public extension Sequence where Element: Hashable {
  func withExclusiveIterations<Iterable: Sequence>(of iterable: Iterable)
  -> [(Element, Iterable.Element)] {
    var iterators: [Element: Iterable.Iterator] = [:]
    return map {
      ($0, iterators[$0, default: iterable.makeIterator()].next()!)
    }
  }
}

[Animal.cat, .dog, .cat, .cat, .dog, .mouse, .dog]
  .withExclusiveIterations(of: 1...)
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