How do you add a Dictionary of items into another Dictionary

Question

Arrays in Swift support the    operator to add the contents of one Array to another  Is there an easy way to do that for a dictionary   eg   var dict1     a     foo   var dict2     b     bar    var combinedDict        some way of combining dict1  amp  dict2 without looping

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It s not built into the Swift library but you can add what you want with operator overloading  e g   func    lt K V gt  left  Dictionary lt K V gt   right  Dictionary lt K V gt        - gt  Dictionary lt K V gt         var map   Dictionary lt K V gt        for  k  v  in left           map k    v           for  k  v  in right           map k    v           return map     This overloads the   operator for Dictionaries which you can now use to add dictionaries with the   operator  e g   var dict1     a     foo   var dict2     b     bar    var dict3   dict1   dict2      a    foo    b    bar

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How about  dict2 forEach    k v  in dict1 k    v     That adds all of dict2 s keys and values into dict1

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Immutable  I prefer to combine unite immutable dictionaries with   operator so I implemented it like      Swift 2 func    lt K V gt   left  Dictionary lt K V gt   right  Dictionary lt K V gt    - gt  Dictionary lt K V gt        guard let right   right else   return left       return left reduce right            var new    0 as  K V          new updateValue  1 1  forKey   1 0          return new          let moreAttributes   String AnyObject      Function   authenticate   let attributes   String AnyObject      File   Auth swift    attributes   moreAttributes   nil     Function    authenticate    File    Auth swift       attributes   moreAttributes     Function    authenticate    File    Auth swift   attributes   nil     File    Auth swift     Mutable     Swift 2 func     lt K V gt   inout left  Dictionary lt K V gt   right  Dictionary lt K V gt          guard let right   right else   return       right forEach   key  value in         left updateValue value  forKey  key           let moreAttributes   String AnyObject      Function   authenticate   var attributes   String AnyObject      File   Auth swift    attributes    nil     File    Auth swift   attributes    moreAttributes     File    Auth swift    Function    authenticate

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Currently  looking at the Swift Standard Library Reference for Dictionary  there is no way to easy update a dictionary with another one   You can write an extension to do it  var dict1     a     foo   var dict2     b     bar    extension Dictionary       mutating func update other Dictionary            for  key value  in other               self updateValue value  forKey key                     dict1 update dict2     dict1 is now   a     foo    b     bar

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You can try this   var dict1     a     foo   var dict2     b     bar    var temp   NSMutableDictionary dictionary  dict1   temp addEntriesFromDictionary dict2

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You can use   func addAll from   String  Any   into   String  Any        from forEach  into  0     1

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Swift 4 provides merging   uniquingKeysWith    so for your case   let combinedDict   dict1 merging dict2     1     The shorthand closure returns  1  therefore dict2 s value will be used when there is a conflict with the keys

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Swift 2 2  func    lt K V gt  left   K   V   right   K   V   - gt   K   V        var result    K V         for  key value  in left           result key    value            for  key value  in right           result key    value           return result

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My needs were different  I needed to merge incomplete nested data sets without clobbering   merging        b    1  2    s   Set  5  6     a   1   d     x   2   with       b    3  4    s   Set  6  7     a   2   d     y   4   yields        b    1  2  3  4    s   Set  5  6  7     a   2   d     y   4   x   2     This was harder than I wanted it to be   The challenge was in mapping from dynamic typing to static typing  and I used protocols to solve this   Also worthy of note is that when you use the dictionary literal syntax  you actually get the foundation types  which do not pick up the protocol extensions   I aborted my efforts to support those as I couldn t find an easy to to validate the uniformity of the collection elements   import UIKit   private protocol Mergable       func mergeWithSame lt T gt  right  T  - gt  T       public extension Dictionary                Merge Dictionaries      - Parameter left  Dictionary to update     - Parameter right   Source dictionary with values to be merged      - Returns  Merged dictionay              func merge right Dictionary  - gt  Dictionary           var merged   self         for  k  rv  in right                   case of existing left value             if let lv   self k                     if let lv   lv as  Mergable where lv dynamicType    rv dynamicType                       let m   lv mergeWithSame rv                      merged k    m                                    else if lv is Mergable                       assert false   Expected common type for matching keys                                       else if   lv is Mergable   let     lv as  NSArray                       assert false   Dictionary literals use incompatible Foundation Types                                      else if   lv is Mergable   let     lv as  NSDictionary                       assert false   Dictionary literals use incompatible Foundation Types                                      else                       merged k    rv                                                     case of no existing value             else                   merged k    rv                                  return merged             extension Array  Mergable        func mergeWithSame lt T gt  right  T  - gt  T             if let right   right as  Array               return  self   right  as  T                    assert false          return nil           extension Dictionary  Mergable        func mergeWithSame lt T gt  right  T  - gt  T             if let right   right as  Dictionary               return self merge right  as  T                    assert false          return nil           extension Set  Mergable        func mergeWithSame lt T gt  right  T  - gt  T             if let right   right as  Set               return self union right  as  T                    assert false          return nil            var dsa12   Dictionary lt String  Any gt    dsa12  a     1 dsa12  b      1  2  dsa12  s     Set  5  6   dsa12  d       c  5   x   2    var dsa34   Dictionary lt String  Any gt    dsa34  a     2 dsa34  b      3  4  dsa34  s     Set  6  7   dsa34  d       c  -5   y   4      let dsa2     a   1   b  a34  let mdsa3   dsa12 merge dsa34  print  merging  n t  dsa12  nwith n t  dsa34   nyields   n t  mdsa3

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You can also use reduce to merge them   Try this in the playground  let d1     a   foo   b   bar   let d2     c   car   d   door    let d3   d1 reduce d2     var d  p  in    d p 0    p 1    return d

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I would just use the Dollar library   https   github com ankurp Dollar  merge---merge-1  Merges all of the dictionaries together and the latter dictionary overrides the value at a given key  let dict  Dictionary lt String  Int gt      Dog   1   Cat   2  let dict2  Dictionary lt String  Int gt      Cow   3  let dict3  Dictionary lt String  Int gt      Sheep   4    merge dict  dict2  dict3    gt    Dog   1   Cat   2   Cow   3   Sheep   4

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I recommend the SwifterSwift Library  However  if you don t want to use the entire library and all its great additions you can just make use of their extension of Dictionary   Swift 3   public extension Dictionary       public static func    lhs  inout  Key  Value   rhs   Key  Value             rhs forEach   lhs  0     1

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In Swift 4  one should use merging   uniquingKeysWith     Example     let dictA     x    1   y   2   z   3  let dictB     x    11   y   22   w   0   let resultA   dictA merging dictB  uniquingKeysWith     first     in first    let resultB   dictA merging dictB  uniquingKeysWith        last  in last     print resultA       x   1   y   2   z   3   w   0  print resultB       x   11   y   22   z   3   w   0

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There is no need extension or any extra func anymore   You can write like that     firstDictionary merge secondDictionary     value1  value2  - gt  AnyObject in         return object2    what you want to return if keys same

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Here is a nice extension I wrote     extension Dictionary where Value  Any       public func mergeOnto target   Key  Value    - gt   Key  Value            guard let target   target else   return self           return self merging target    current    in current             to use   var dict1     cat   5   dog   6  var dict2     dog   9   rodent   10   dict1   dict1 mergeOnto target  dict2    Then  dict1 will be modified to    cat   5   dog   6   rodent   10

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Swift 3  dictionary extension   public extension Dictionary        public static func    lhs  inout Dictionary  rhs  Dictionary            for  k  v  in rhs               lhs k    v

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You can iterate over the Key Value combinations ob the value you want to merge and add them  via the updateValue forKey   method   dictionaryTwo forEach       dictionaryOne updateValue  1  forKey   0      Now all values of dictionaryTwo got added to dictionaryOne

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You can define    operator for Dictionary  e g    func     lt K  V gt   left  inout  K V   right   K V          for  k  v  in right            left k    v

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Swift 2 0  extension Dictionary        mutating func unionInPlace dictionary  Dictionary            dictionary forEach   self updateValue  1  forKey   0               func union var dictionary  Dictionary  - gt  Dictionary           dictionary unionInPlace self          return dictionary

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The same as  farhadf s answer but adopted for Swift 3   let sourceDict1    1   one   2   two   let sourceDict2    3   three   4   four    let result   sourceDict1 reduce sourceDict2     partialResult   pair  in     var partialResult   partialResult   without this line we could not modify the dictionary     partialResult pair 0    pair 1     return partialResult

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You can use the bridgeToObjectiveC   function to make the dictionary a NSDictionary    Will be like the following   var dict1     a   Foo   var dict2     b   Boo    var combinedDict   dict1 bridgeToObjectiveC   var mutiDict1   NSMutableDictionary    combinedDict mutableCopy   as NSMutableDictionary  var combineDict2   dict2 bridgeToObjectiveC    var combine   mutiDict1 addEntriesFromDictionary combineDict2    Then you can convert the NSDictionary combine  back or do whatever

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You can add a Dictionary extension like this   extension Dictionary       func mergedWith otherDictionary   Key  Value   - gt   Key  Value            var mergedDict   Key  Value                 self  otherDictionary  forEach   dict in             for  key  value  in dict                   mergedDict key    value                                 return mergedDict           Then usage is as simple as the following   var dict1     a     foo   var dict2     b     bar    var combinedDict   dict1 mergedWith dict2       gt    a    foo    b    bar       If you prefer a framework that also includes some more handy features then checkout HandySwift  Just import it to your project and you can use the above code without adding any extensions to the project yourself

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Swift 3   extension Dictionary        mutating func merge with dictionary  Dictionary            dictionary forEach   updateValue  1  forKey   0               func merged with dictionary  Dictionary  - gt  Dictionary           var dict   self         dict merge with  dictionary          return dict          let a     a   b   let b     1   2   let c   a merged with  b   print c      a    b    1    2

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A more readable variant using an extension    extension Dictionary           func merge dict  Dictionary lt Key Value gt   - gt  Dictionary lt Key Value gt            var mutableCopy   self                 for  key  value  in dict                  If both dictionaries have a value for same key  the value of the other dictionary is used                         mutableCopy key    value                            return mutableCopy

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import Foundation  let x     a  1  let y     b  2   let out   NSMutableDictionary dictionary  x  out addEntriesFromDictionary y    The result is an NSMutableDictionary not a Swift typed dictionary  but the syntax to use it is the same  out  a      1 in this case  so you d only have a problem if you re using third-party code which expects a Swift dictionary  or really need the type checking   The short answer here is that you actually do have to loop  Even if you re not entering it explicitly  that s what the method you re calling  addEntriesFromDictionary  here  will do  I d suggest if you re a bit unclear on why that would be the case you should consider how you would merge the leaf nodes of two B-trees   If you really actually need a Swift native dictionary type in return  I d suggest   let x     a  1  let y     b  2   var out   x for  k  v  in y       out k    v     The downside of this approach is that the dictionary index - however it s done - may be rebuilt several times in the loop  so in practice this is about 10x slower than the NSMutableDictionary approach

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All of these responses are complicated  This is my solution for swift 2 2          get first dictionnary     let finalDictionnary   NSMutableDictionary   self getBasicDict         cast second dictionnary as  NSObject   AnyObject      let secondDictionnary    NSObject   AnyObject    self getOtherDict   as  NSObject   AnyObject        merge dictionnary into the first one     finalDictionnary addEntriesFromDictionary secondDictionnary

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No need to have any dictionary extensions now  Swift Xcode 9 0   dictionary has got a functionality for this  Have a look here  Below here is an example on how to use it    var oldDictionary     a   1   b   2    var newDictionary     a   10000   b   10000   c   4     oldDictionary merge newDictionary     oldValue  newValue  - gt  Int in            This closure return what value to consider if repeated keys are found         return newValue        print oldDictionary     Prints   b   10000   a   10000   c   4

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Some even more streamlined overloads for Swift 4   extension Dictionary       static func     lhs  inout  Key Value   rhs   Key Value             lhs merge rhs   1            static func    lhs   Key Value   rhs   Key Value   - gt   Key Value            return lhs merging rhs   1

[dictionary] How do you add a Dictionary of items into another Dictionary

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