Iterating Through a Dictionary in Swift

Question

I am a little confused on the answer that Xcode is giving me to this experiment in the Swift Programming Language Guide      Use a for-in to iterate through a dictionary  experiment   let interestingNumbers          Prime    2  3  5  7  11  13        Fibonacci    1  1  2  3  5  8        Square    1  4  9  16  25    var largest   0 for  kind  numbers  in interestingNumbers       for number in numbers           if number  gt  largest               largest   number                   largest   I understand that as the dictionary is being transversed  the largest number is being set to the variable  largest  However  I am confused as to why Xcode is saying that largest is being set 5 times  or 1 time  or 3 times  depending on each test    When looking through the code  I see that it should be set 6 times in  Prime  alone  2  3  5  7  11  13   Then it should skip over any numbers in  Fibonacci  since those are all less than the largest  which is currently set to 13 from  Prime   Then  it should be set to 16  and finally 25 in  Square   yielding a total of 8 times    Am I missing something entirely obvious

User · Answer

let dict    String   Any      FirstName     Maninder     LastName     Singh     Address     Chandigarh   dict forEach   print  0      Result would be    FirstName    Maninder     LastName    Singh     Address    Chandigarh

User · Answer

Arrays are ordered collections but dictionaries and sets are unordered collections  Thus you can t predict the order of iteration in a dictionary or a set   Read this article to know more about  Collection Types  Swift Programming Language

User · Answer

Here is an alternative for that experiment  Swift 3 0   This tells you exactly which kind of number was the largest   let interestingNumbers      Prime    2  3  5  7  11  13    Fibonacci    1  1  2  3  5  8    Square    1  4  9  16  25      var largest   0 var whichKind  String    nil  for  kind  numbers  in interestingNumbers       for number in numbers       if number  gt  largest           whichKind   kind         largest   number              print whichKind  print largest   OUTPUT  Optional  Square   25

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Dictionaries in Swift  and other languages  are not ordered  When you iterate through the dictionary  there s no guarentee that the order will match the initialization order  In this example  Swift processes the  Square  key before the others  You can see this by adding a print statement to the loop  25 is the 5th element of Square so largest would be set 5 times for the 5 elements in Square and then would stay at 25   let interestingNumbers          Prime    2  3  5  7  11  13        Fibonacci    1  1  2  3  5  8        Square    1  4  9  16  25    var largest   0 for  kind  numbers  in interestingNumbers       println  kind    kind        for number in numbers           if number  gt  largest               largest   number                   largest   This prints    kind  Square kind  Prime kind  Fibonacci

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If you want to iterate over all the values   dict values forEach   value in        print value

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This is a user-defined function to iterate through a dictionary     func findDic dict   String  String        for  key  value  in dict      print    key      value           findDic dict    Animal   Lion    Bird   Sparrow      prints Animal   Lion           Bird   Sparrow

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You can also use values makeIterator   to iterate over dict values  like this  for sb in sbItems values makeIterator         do something with your sb item     print sb     You can also do the iteration like this  in a more swifty style  sbItems values makeIterator   forEach        0 is your dict value     print  0      sbItems is dict of type  String   NSManagedObject

[dictionary] Iterating Through a Dictionary in Swift

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