Swift how to sort array of custom objects by property value

Question

lets say we have a custom class named imageFile and this class contains two properties    class imageFile        var fileName   String       var fileID   Int       lots of them stored in Array  var images   Array       var aImage   imageFile   aImage fileName    image1 png  aImage fileID   101 images append aImage   aImage   imageFile   aImage fileName    image1 png  aImage fileID   202 images append aImage    question is  how can i sort images array by  fileID  ASC or DESC

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Sort using KeyPath you can sort by KeyPath like this  myArray sorted by    fileName   lt      using   lt   for ascending sorting     By implementing this little helpful extension  extension Collection      func sorted lt Value  Comparable gt           by keyPath  KeyPath lt Element  Value gt             comparator     lhs  Value    rhs  Value  - gt  Bool  - gt   Element            sorted   comparator  0 keyPath  keyPath    1 keyPath  keyPath              Hope Swift add this in the near future in the core of the language

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Updated for Swift 3 with sort by    This  exploiting a trailing closure   images sorted    0 fileID  lt   1 fileID     where you use  lt  or  gt  depending on ASC or DESC  respectively   If you want to modify the images array  then use the following   images sort    0 fileID  lt   1 fileID     If you are going to do this repeatedly and prefer to define a function  one way is   func sorterForFileIDASC this imageFile  that imageFile  - gt  Bool     return this fileID  gt  that fileID     and then use as   images sort by  sorterForFileIDASC

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If you want to sort original array of custom objects  Here is another way to do so in Swift 2 1  var myCustomerArray    Customer    myCustomerArray sortInPlace   customer1 Customer  customer2 Customer  - gt  Bool in     customer1 id  lt  customer2 id     Where id is an Integer  You can use the same  lt  operator for String properties as well   You can learn more about its use by looking at an example here  Swift2  Nearby Customers

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You can also do something like  images   sorted images    0 fileID  gt   1 fileID    so your images array will be stored as sorted

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If you are going to be sorting this array in more than one place  it may make sense to make your array type Comparable   class MyImageType  Comparable  Printable       var fileID  Int         For Printable     var description  String           get               return  ID    fileID                        init fileID  Int            self fileID   fileID             For Comparable func  lt  left  MyImageType  right  MyImageType  - gt  Bool       return left fileID  lt  right fileID       For Comparable func    left  MyImageType  right  MyImageType  - gt  Bool       return left fileID    right fileID    let one   MyImageType fileID  1  let two   MyImageType fileID  2  let twoA   MyImageType fileID  2  let three   MyImageType fileID  3   let a1    one  three  two      return a sorted array println sorted a1        ID  1  ID  2  ID  3    var a2    two  one  twoA  three      sort the array  in place  sort  amp a2  println a2       ID  1  ID  2  ID  2  ID  3

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Two alternatives  1  Ordering the original array with sortInPlace  self assignments sortInPlace    0 order  lt   1 order    self printAssignments assignments    2  Using an alternative array to store the ordered array  var assignmentsO    Assignment     assignmentsO   self assignments sort    0 order  lt   1 order    self printAssignments assignmentsO

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I do it like this and it works   var images    imageFile        images sorted by    0 fileID compare  1 fileID      orderedAscending

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Swift 3  people   people sorted by     0 email  gt   1 email

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With Swift 5  Array has two methods called sorted   and sorted by    The first method  sorted    has the following declaration      Returns the elements of the collection  sorted    func sorted   - gt   Element    The second method  sorted by    has the following declaration      Returns the elements of the collection  sorted using the given predicate as the comparison between elements    func sorted by areInIncreasingOrder   Element  Element  throws - gt  Bool  rethrows - gt   Element       1  Sort with ascending order for comparable objects  If the element type inside your collection conforms to Comparable protocol  you will be able to use sorted   in order to sort your elements with ascending order  The following Playground code shows how to use sorted     class ImageFile  CustomStringConvertible  Comparable        let fileName  String     let fileID  Int     var description  String   return  ImageFile with ID    fileID          init fileName  String  fileID  Int            self fileName   fileName         self fileID   fileID            static func    lhs  ImageFile  rhs  ImageFile  - gt  Bool           return lhs fileID    rhs fileID            static func  lt  lhs  ImageFile  rhs  ImageFile  - gt  Bool           return lhs fileID  lt  rhs fileID           let images         ImageFile fileName   Car   fileID  300       ImageFile fileName   Boat   fileID  100       ImageFile fileName   Plane   fileID  200     let sortedImages   images sorted   print sortedImages       prints   ImageFile with ID  100  ImageFile with ID  200  ImageFile with ID  300           2  Sort with descending order for comparable objects  If the element type inside your collection conforms to Comparable protocol  you will have to use sorted by   in order to sort your elements with a descending order   class ImageFile  CustomStringConvertible  Comparable        let fileName  String     let fileID  Int     var description  String   return  ImageFile with ID    fileID          init fileName  String  fileID  Int            self fileName   fileName         self fileID   fileID            static func    lhs  ImageFile  rhs  ImageFile  - gt  Bool           return lhs fileID    rhs fileID            static func  lt  lhs  ImageFile  rhs  ImageFile  - gt  Bool           return lhs fileID  lt  rhs fileID           let images         ImageFile fileName   Car   fileID  300       ImageFile fileName   Boat   fileID  100       ImageFile fileName   Plane   fileID  200     let sortedImages   images sorted by     img0  ImageFile  img1  ImageFile  - gt  Bool in     return img0  gt  img1      let sortedImages   images sorted by   gt      also works   let sortedImages   images sorted    0  gt   1      also works print sortedImages       prints   ImageFile with ID  300  ImageFile with ID  200  ImageFile with ID  100           3  Sort with ascending or descending order for non-comparable objects  If the element type inside your collection DOES NOT conform to Comparable protocol  you will have to use sorted by   in order to sort your elements with ascending or descending order   class ImageFile  CustomStringConvertible        let fileName  String     let fileID  Int     var description  String   return  ImageFile with ID    fileID          init fileName  String  fileID  Int            self fileName   fileName         self fileID   fileID           let images         ImageFile fileName   Car   fileID  300       ImageFile fileName   Boat   fileID  100       ImageFile fileName   Plane   fileID  200     let sortedImages   images sorted by     img0  ImageFile  img1  ImageFile  - gt  Bool in     return img0 fileID  lt  img1 fileID      let sortedImages   images sorted    0 fileID  lt   1 fileID      also works print sortedImages       prints   ImageFile with ID  300  ImageFile with ID  200  ImageFile with ID  100          Note that Swift also provides two methods called sort   and sort by   as counterparts of sorted   and sorted by   if you need to sort your collection in-place

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Swift 2 through 4  The original answer sought to sort an array of custom objects using some property  Below I will show you a few handy ways to do this same behavior w  swift data structures   Little things outta the way  I changed ImageFile ever so slightly  With that in mind  I create an array with three image files  Notice that metadata is an optional value  passing in nil as a parameter is expected    struct ImageFile         var name  String       var metadata  String        var size  Int            var images   ImageFile     ImageFile name   HelloWorld   metadata  nil  size  256   ImageFile name   Traveling Salesmen   metadata   uh this is huge   size  1024   ImageFile name   Slack   metadata   what s in this stuff    size  2048      ImageFile has a property named size  For the following examples I will show you how to use sort operations w  properties like size    smallest to biggest size   lt          let sizeSmallestSorted   images sorted    initial  next  - gt  Bool in       return initial size  lt  next size         biggest to smallest          let sizeBiggestSorted   images sorted    initial  next  - gt  Bool in       return initial size  gt  next size         Next we ll sort using the String property name  In the same manner  use sort to compare strings  But notice the inner block returns a comparison result  This result will define sort   A-Z   orderedAscending       let nameAscendingSorted   images sorted    initial  next  - gt  Bool in       return initial name compare next name      orderedAscending         Z-A   orderedDescending       let nameDescendingSorted   images sorted    initial  next  - gt  Bool in       return initial name compare next name      orderedDescending         Next is my favorite way to sort  in many cases one will have optional properties  Now don t worry  we re going to sort in the same manner as above except we have to handle nil  In production    I used this code to force all instances in my array with nil property values to be last  Then order metadata using the assumed unwrapped values       let metadataFirst   images sorted    initial  next  - gt  Bool in       guard initial metadata    nil else   return true         guard next metadata    nil else   return true         return initial metadata  compare next metadata       orderedAscending         It is possible to have a secondary sort for optionals  For example  one could show images with metadata and ordered by size

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Swift 3  amp  4  amp  5  I had some problem related to lowercase and capital case   so I did this code   let sortedImages   images sorted by     0 fileID lowercased    lt   1 fileID lowercased        and then use sortedImages after that

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Swift 4 0  4 1  amp  4 2 First  I created mutable array of type imageFile   as shown below  var arr    imageFile      Create mutable object image of type imageFile   and assign value to properties as shown below     var image   imageFile      image fileId   14    image fileName    A    Now  append this object to array arr      arr append image    Now  assign the different properties to same mutable object i e image     image   imageFile      image fileId   13    image fileName    B    Now  again append image object to array arr      arr append image    Now  we will apply Ascending order on fileId property in array arr objects  Use  lt  symbol for Ascending order   arr   arr sorted by    0 fileId  lt   1 fileId      arr has all objects in Ascending order  print  sorted array is  arr 0  fileId    sorted array is 13  print  sorted array is  arr 1  fileId   sorted array is 14   Now  we will apply Descending order on on fileId property in array arr objects  Use   symbol for Descending order   arr   arr sorted by    0 fileId  gt   1 fileId      arr has all objects in Descending order  print  Unsorted array is  arr 0  fileId    Unsorted array is 14  print  Unsorted array is  arr 1  fileId    Unsorted array is 13   In Swift 4 1   amp  4 2 For sorted order use  let sortedArr   arr sorted    id1  id2  - gt  Bool in   return id1 fileId  lt  id2 fileId    Use  gt  for Descending order

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You return a sorted array from the fileID property by following way   Swift 2  let sortedArray   images sorted    0 fileID  gt   1 fileID      Swift 3 OR 4  let sortedArray   images sorted by     0 fileID  gt   1 fileID      Swift 5 0  let sortedArray   images sorted        0 fileID  lt   1 fileID

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First  declare your Array as a typed array so that you can call methods when you iterate   var images    imageFile         Then you can simply do   Swift 2  images sorted    0 fileID  gt   1 fileID      Swift 3   images sorted by     0 fileID  gt   1 fileID      The example above gives desc sort order

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If you are not using custom objects  but value types instead that implements Comparable protocol  Int  String etc    you can simply do this   myArray sort  gt     sort descending order   An example   struct MyStruct  Comparable       var name    Untitled     func  lt  lhs  MyStruct  rhs  MyStruct  - gt  Bool       return lhs name  lt  rhs name      Implementation of    required by Equatable func    lhs  MyStruct  rhs  MyStruct  - gt  Bool       return lhs name    rhs name    let value1   MyStruct   var value2   MyStruct    value2 name    A New Name   var anArray  MyStruct       anArray append value1  anArray append value2   anArray sort  gt      This will sort the array in descending order

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In Swift 3 0  images sort by     first  imageFile  second  imageFile  - gt  Bool in     first  fileID  lt  second  fileID

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var students     Kofi    Abena    Peter    Kweku    Akosua    students sort by   gt    print students    Prints      Peter    Kweku    Kofi    Akosua    Abena

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Nearly everyone gives how directly  let me show the evolvement   you can use the instance methods of Array      general form of closure images sortInPlace    image1  imageFile  image2  imageFile  - gt  Bool in return image1 fileID  gt  image2 fileID        types of closure s parameters and return value can be inferred by Swift  so they are omitted along with the return arrow  - gt   images sortInPlace   image1  image2 in return image1 fileID  gt  image2 fileID        Single-expression closures can implicitly return the result of their single expression by omitting the  return  keyword images sortInPlace   image1  image2 in image1 fileID  gt  image2 fileID        closure s argument list along with  in  keyword can be omitted   0   1   2  and so on are used to refer the closure s first  second  third arguments and so on images sortInPlace    0 fileID  gt   1 fileID        the simplification of the closure is the same images   images sort    image1  imageFile  image2  imageFile  - gt  Bool in return image1 fileID  gt  image2 fileID    images   images sort   image1  image2 in return image1 fileID  gt  image2 fileID    images   images sort   image1  image2 in image1 fileID  gt  image2 fileID    images   images sort    0 fileID  gt   1 fileID      For elaborate explanation about the working principle of sort  see The Sorted Function

[arrays] Swift how to sort array of custom objects by property value

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