How to iterate a loop with index and element in Swift

Question

Is there a function that I can use to iterate over an array and have both index and element  like Python s enumerate  for index  element in enumerate list

User · Answer

Using  enumerate   works  but it does not provide the true index of the element  it only provides an Int beginning with 0 and incrementing by 1 for each successive element  This is usually irrelevant  but there is the potential for unexpected behavior when used with the ArraySlice type  Take the following code   let a     a    b    c    d    e   a indices     gt  0   lt 5  let aSlice   a 1   lt 4      gt  ArraySlice with   b    c    d   aSlice indices     gt  1   lt 4  var test    Int  String    for  index  element  in aSlice enumerate         test index    element   test     gt   0   b   1   c   2   d      indices presented as 0   lt 3  but they are actually 1   lt 4 test 0     aSlice 0     ERROR  out of bounds   It s a somewhat contrived example  and it s not a common issue in practice but still I think it s worth knowing this can happen

User · Answer

Starting with Swift 2  the enumerate function needs to be called on the collection like so   for  index  element  in list enumerate         print  Item   index     element

User · Answer

Swift 5 provides a method called enumerated   for Array  enumerated   has the following declaration   func enumerated   - gt  EnumeratedSequence lt Array lt Element gt  gt       Returns a sequence of pairs  n  x   where n represents a consecutive integer starting at zero and x represents an element of the sequence      In the simplest cases  you may use enumerated   with a for loop  For example   let list     Car    Bike    Plane    Boat   for  index  element  in list enumerated         print index       element        prints  0   Car 1   Bike 2   Plane 3   Boat        Note however that you re not limited to use enumerated   with a for loop  In fact  if you plan to use enumerated   with a for loop for something similar to the following code  you re doing it wrong   let list    Int  1   5  var arrayOfTuples     Int  Int      for  index  element  in list enumerated         arrayOfTuples      index  element      print arrayOfTuples     prints   0  1    1  2    2  3    3  4    4  5     A swiftier way to do this is   let list    Int  1   5  let arrayOfTuples   Array list enumerated    print arrayOfTuples     prints   offset  0  element  1    offset  1  element  2    offset  2  element  3    offset  3  element  4    offset  4  element  5       As an alternative  you may also use enumerated   with map   let list    Int  1   5  let arrayOfDictionaries   list enumerated   map    a  b  in return  a   b    print arrayOfDictionaries     prints   0  1    1  2    2  3    3  4    4  5       Moreover  although it has some limitations  forEach can be a good replacement to a for loop   let list    Int  1   5  list reversed   enumerated   forEach   print  0        1        prints  0   5 1   4 2   3 3   2 4   1        By using enumerated   and makeIterator    you can even iterate manually on your Array  For example   import UIKit import PlaygroundSupport  class ViewController  UIViewController        var generator     Car    Bike    Plane    Boat   enumerated   makeIterator        override func viewDidLoad             super viewDidLoad            let button   UIButton type   system          button setTitle  Tap   for   normal          button frame   CGRect x  100  y  100  width  100  height  100          button addTarget self  action   selector iterate       for   touchUpInside          view addSubview button              objc func iterate   sender  UIButton            let tuple   generator next           print String describing  tuple             PlaygroundPage current liveView   ViewController        Optional  offset  0  element   Car     Optional  offset  1  element   Bike     Optional  offset  2  element   Plane     Optional  offset  3  element   Boat     nil  nil  nil

User · Answer

For what you are wanting to do  you should use the enumerated   method on your Array   for  index  element  in list enumerated         print    index  -   element

User · Answer

We called enumerate function to implements this  like     for  index  element  in array enumerate          index is indexposition of array      element is element of array

User · Answer

For those who want to use forEach   Swift 4  extension Array     func forEachWithIndex   body   Int  Element  throws - gt  Void  rethrows       try zip  startIndex    lt  endIndex   self  forEach body          Or  array enumerated   forEach

User · Answer

Starting with Swift 3  it is   for  index  element  in list enumerated       print  Item   index     element

User · Answer

Basic enumerate  for  index  element  in arrayOfValues enumerate        do something useful     or with Swift 3     for  index  element  in arrayOfValues enumerated        do something useful     Enumerate  Filter and Map  However  I most often use enumerate in combination with map or filter  For example with operating on a couple of arrays   In this array I wanted to filter odd or even indexed elements and convert them from Ints to Doubles  So enumerate   gets you index and the element  then filter checks the index  and finally to get rid of the resulting tuple I map it to just the element   let evens   arrayOfValues enumerate   filter                                index  Int  element  Int  - gt  Bool in                             return index   2    0                            map       Int  element  Int  - gt  Double in                             return Double element                             let odds   arrayOfValues enumerate   filter                                index  Int  element  Int  - gt  Bool in                             return index   2    0                            map       Int  element  Int  - gt  Double in                             return Double element

User · Answer

This is the Formula of loop of Enumeration   for  index  value  in shoppingList enumerate     print  Item   index   1     value        for more detail you can check Here

User · Answer

Xcode 8 and Swift 3   Array can be enumerated using tempArray enumerated    Example   var someStrs    String     someStrs append  Apple     someStrs append  Amazon     someStrs      Google         for  index  item  in someStrs enumerated                 print  Value at index     index  is   item           console   Value at index   0 is Apple Value at index   1 is Amazon Value at index   2 is Google

User · Answer

Yes  As of Swift 3 0  if you need the index for each element along with its value  you can use the enumerated   method to iterate over the array  It returns a sequence of pairs composed of the index and the value for each item in the array  For example   for  index  element  in list enumerated       print  Item   index     element        Before Swift 3 0 and after Swift 2 0  the function was called enumerate     for  index  element  in list enumerate         print  Item   index     element        Prior to Swift 2 0  enumerate was a global function   for  index  element  in enumerate list        println  Item   index     element

User · Answer

You can simply use loop of enumeration to get your desired result   Swift 2   for  index  element  in elements enumerate         print    index     element        Swift 3  amp  4   for  index  element  in elements enumerated         print    index     element        Or you can simply go through a for loop to get the same result   for index in 0   lt elements count       let element   elements index      print    index     element        Hope it helps

User · Answer

Use  enumerated   like this in functional programming  list enumerated   forEach   print  0 offset   0 element

User · Answer

Swift 5 x  I personally prefer using the forEach method  list enumerated   forEach    index  element  in            You can also use the short version  list enumerated   forEach   print  quot index     0 0   value     0 1  quot

User · Answer

For completeness you can simply iterate over your array indices and use subscript to access the element at the corresponding index  let list    100 200 300 400 500  for index in list indices       print  quot Element at  quot   index   quot  Value  quot   list index      Using forEach list indices forEach       print  quot Element at  quot    0   quot  Value  quot   list  0      Using collection enumerated   method  Note that it returns a collection of tuples with the offset and the element  for item in list enumerated         print  quot Element at  quot   item offset   quot  Value  quot   item element     using forEach  list enumerated   forEach       print  quot Element at  quot    0 offset   quot  Value  quot    0 element      Those will print  Element at  0  Value  100 Element at  1  Value  200 Element at  2  Value  300 Element at  3  Value  400 Element at  4  Value  500  If you need the array index  not the offset  and its element you can extend Collection and create your own method to get the indexed elements  extension Collection       func indexedElements body    index  Index  element  Element   throws - gt  Void  rethrows           var index   startIndex         for element in self               try body  index element               formIndex after   amp index                      Another possible implementation as suggested by Alex is to zip the collection indices with its elements  extension Collection       func indexedElements body    index  Index  element  Element   throws - gt  Void  rethrows           for element in zip indices  self    try body element              var indexedElements  Zip2Sequence lt Indices  Self gt    zip indices  self        Testing  let list      quot 100 quot   quot 200 quot   quot 300 quot   quot 400 quot   quot 500 quot       You can iterate the index and its elements using a closure list dropFirst 2  indexedElements       print  quot Index  quot    0 index   quot Element  quot    0 element        or using a for loop for  index  element  in list indexedElements        print  quot Index  quot   index   quot Element  quot   element     This will p rint  Index  2 Element  300 Index  3 Element  400 Index  4 Element  500 Index  0 Element  100 Index  1 Element  200 Index  2 Element  300 Index  3 Element  400 Index  4 Element  500

User · Answer

I found this answer while looking for a way to do that with a Dictionary  and it turns out it s quite easy to adapt it  just pass a tuple for the element      Swift 2  var list     a   1   b   2   for  index   letter  value   in list enumerate         print  Item   index     letter    value

[arrays] How to iterate a loop with index and element in Swift

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