How can I run through three separate arrays in the same for loop?

by

This is a very common requirement so the standard library caters to it with a function, zip:*

for (a,b) in zip(seq1, seq2) {
    // a and b will be matching pairs from the two sequences
}

Unfortunately, as of right now, zip only does pairs, even though in theory it could be overloaded to do triples. However, it’s not a big deal, you can just nest them:

var names = ["Joe", "Sarah", "Chad"]
var ages = [18, 20, 22]
var genders: [Gender] = [.Male, .Female, .Male]

for (name,(age,gender)) in zip(names,zip(ages,genders)) {
    makeUser(name, userAge: age, userGender: gender)
}

Note, it will only serve up to the shortest sequence, so if there are more names than ages or genders, you’ll only get the matching names.

This might seem like a down side compared to using an index, and this might also seem more complex, but the alternative’s simplicity is deceptive. Bear in mind what would happen if you used indices or enumerate alongside arrays that didn’t match – you’d get an array out of bounds assertion (or you’d have to put in checking logic).

zip avoids this problem. It also means you can use sequences instead of collections, as well as working with collections that don’t have integer indices (unlike enumerate) or collections that have different index types (e.g. a String and an Array).

*(in the current beta, anyway – zip returns a Zip2 object. In Swift 1.1, you need to create the Zip2 version directly as zip has only just been introduced)

More Related Contents:

  1. how to check if there is any string from index 0 to 5 in an array of type Any [closed]
  2. remove an index number from array
  3. How to find index of list item in Swift?
  4. Get random elements from array in Swift
  5. Swift: Creating an Array with a Default Value of distinct object instances
  6. Two-dimensional array in Swift
  7. Why isn’t [SomeStruct] convertible to [Any]?
  8. How can I extend typed Arrays in Swift?
  9. Making my function calculate average of array Swift
  10. Converting a C char array to a String
  11. Sorting a Swift array by ordering from another array
  12. Confused about Swift Array Declarations
  13. Finding sum of elements in Swift array
  14. Swift 3.0: compiler error when calling global func min(T,T) in Array or Dictionary extension
  15. Count the occurences a particular integer has in an array [duplicate]
  16. Swift 3 2d array of Int
  17. type any? has no subscript members
  18. How to split a string by new lines in Swift
  19. How can I interleave two arrays?
  20. Convert bytes/UInt8 array to Int in Swift
  21. Compare arrays in swift
  22. Swift: What’s the best way to pair up elements of an Array
  23. Swift 4 JSON Codable – value returned is sometimes an object, others an array
  24. Multidimensional arrays in Swift
  25. Extending Array to check if it is sorted in Swift?
  26. How can I convert an array to a tuple?
  27. How to return first 5 objects of Array in Swift?
  28. What does $0 and $1 mean in Swift Closures?
  29. How to forward functions with variadic parameters?
  30. Swift: Binary search for standard array?

Leave a Comment