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Showing content from https://www.mongodb.com/docs/realm-sdks/swift/latest/Protocols/RealmKeyedCollection.html below:

RealmKeyedCollection Protocol Reference

RealmKeyedCollection

public protocol RealmKeyedCollection : ThreadConfined, CustomStringConvertible, Sequence

A homogenous key-value collection of Objects which can be retrieved, filtered, sorted, and operated upon.

The type of key associated with this collection
Declaration
Swift
```
associatedtype Key : _MapKey
```
The type of value associated with this collection.

The Realm which manages the map, or nil if the map is unmanaged.
Declaration
Swift
```
var realm: Realm? { get }
```
Indicates if the map can no longer be accessed.
Declaration
Swift
```
var isInvalidated: Bool { get }
```
Returns the number of key-value pairs in this map.
Declaration
Swift
```
var count: Int { get }
```
A human-readable description of the objects contained in the Map.
Declaration
Swift
```
var description: String { get }
```

Updates the value stored in the dictionary for the given key, or adds a new key-value pair if the key does not exist.

Note

Note:If the value being added to the dictionary is an unmanaged object and the dictionary is managed then that unmanaged object will be added to the Realm.

Warning

This method may only be called during a write transaction.
Declaration
Swift
```
func updateValue(_ value: Value, forKey key: Key)
```
Parameters value
a value’s key path predicate.
forKey
The direction to sort in.
Removes the given key and its associated object, only if the key exists in the dictionary. If the key does not exist, the dictionary will not be modified.

Warning
Declaration
Swift
```
func removeObject(for key: Key)
```
Removes all objects from the dictionary. The objects are not removed from the Realm that manages them.

Warning
Returns the value for a given key, or sets a value for a key should the subscript be used for an assign.

Note

Note:If the value being added to the dictionary is an unmanaged object and the dictionary is managed then that unmanaged object will be added to the Realm.

Note

Note:If the value being assigned for a key is nil then that key will be removed from the dictionary.

Warning

This method may only be called during a write transaction.
Declaration
Swift
```
subscript(key: Key) -> Value? { get set }
```

Returns a type of Value for a specified key if it exists in the map.

Note that when using key-value coding, the key must be a string.
Declaration
Swift
```
func value(forKey key: String) -> AnyObject?
```
Parameters key
The key to the property whose values are desired.
Returns a type of Value for a specified key if it exists in the map.
Declaration
Swift
```
func value(forKeyPath keyPath: String) -> AnyObject?
```
Parameters keyPath
The key to the property whose values are desired.
Adds a given key-value pair to the dictionary or updates a given key should it already exist.

Warning

This method can only be called during a write transaction.
Declaration
Swift
```
func setValue(_ value: Any?, forKey key: String)
```
Parameters value
The object value.
key
The name of the property whose value should be set on each object.

Returns a Results containing all matching values in the dictionary with the given predicate.

Note

This will return the values in the dictionary, and not the key-value pairs.
Declaration
Swift
```
func filter(_ predicate: NSPredicate) -> Results<Value>
```
Parameters predicate
The predicate with which to filter the values.
Returns a Boolean value indicating whether the Map contains the key-value pair satisfies the given predicate
Declaration
Swift
```
func contains(where predicate: @escaping (_ key: Key, _ value: Value) -> Bool) -> Bool
```
Parameters where
a closure that test if any key-pair of the given map represents the match.

Returns a Results containing the objects in the dictionary, but sorted.

Objects are sorted based on their values. For example, to sort a dictionary of Dates from neweset to oldest based, you might call dates.sorted(ascending: true).
Parameters ascending
The direction to sort in.
Returns a Results containing the objects in the dictionary, but sorted.

Objects are sorted based on the values of the given key path. For example, to sort a dictionary of Students from youngest to oldest based on their age property, you might call students.sorted(byKeyPath: "age", ascending: true).

Warning

Dictionaries may only be sorted by properties of boolean, Date, NSDate, single and double-precision floating point, integer, and string types.
Declaration
Swift
```
func sorted(byKeyPath keyPath: String, ascending: Bool) -> Results<Value>
```
Parameters keyPath
The key path to sort by.
ascending
The direction to sort in.
Returns a Results containing the objects in the dictionary, but sorted.

Warning

Dictionaries may only be sorted by properties of boolean, Date, NSDate, single and double-precision floating point, integer, and string types.
Returns all of the keys in this dictionary.
Declaration
Swift
```
var keys: [Key] { get }
```
Returns all of the values in the dictionary.
Declaration
Swift
```
var values: [Value] { get }
```

Returns the minimum (lowest) value of the given property among all the objects in the collection, or nil if the dictionary is empty.

Warning

Only a property whose type conforms to the MinMaxType protocol can be specified.
Declaration
Swift
```
func min<T>(ofProperty property: String) -> T? where T : _HasPersistedType, T.PersistedType : MinMaxType
```
Parameters property
The name of a property whose minimum value is desired.
Returns the maximum (highest) value of the given property among all the objects in the dictionary, or nil if the dictionary is empty.

Warning

Only a property whose type conforms to the MinMaxType protocol can be specified.
Declaration
Swift
```
func max<T>(ofProperty property: String) -> T? where T : _HasPersistedType, T.PersistedType : MinMaxType
```
Parameters property
The name of a property whose minimum value is desired.
Returns the sum of the given property for objects in the dictionary, or nil if the dictionary is empty.

Warning

Only names of properties of a type conforming to the AddableType protocol can be used.
Declaration
Swift
```
func sum<T>(ofProperty property: String) -> T where T : _HasPersistedType, T.PersistedType : AddableType
```
Parameters property
The name of a property conforming to AddableType to calculate sum on.
Returns the average value of a given property over all the objects in the dictionary, or nil if the dictionary is empty.

Warning

Only a property whose type conforms to the AddableType protocol can be specified.
Declaration
Swift
```
func average<T>(ofProperty property: String) -> T? where T : _HasPersistedType, T.PersistedType : AddableType
```
Parameters property
The name of a property whose values should be summed.

Registers a block to be called each time the dictionary changes.

The block will be asynchronously called with the initial dictionary, and then called again after each write transaction which changes either any of the keys or values in the dictionary.

The change parameter that is passed to the block reports, in the form of keys within the dictionary, which of the key-value pairs were added, removed, or modified during each write transaction.

At the time when the block is called, the dictionary will be fully evaluated and up-to-date, and as long as you do not perform a write transaction on the same thread or explicitly call realm.refresh(), accessing it will never perform blocking work.

If no queue is given, notifications are delivered via the standard run loop, and so can’t be delivered while the run loop is blocked by other activity. If a queue is given, notifications are delivered to that queue instead. When notifications can’t be delivered instantly, multiple notifications may be coalesced into a single notification. This can include the notification with the initial collection.

For example, the following code performs a write transaction immediately after adding the notification block, so there is no opportunity for the initial notification to be delivered first. As a result, the initial notification will reflect the state of the Realm after the write transaction.
```
let myStringMap = myObject.stringMap
print("myStringMap.count: \(myStringMap?.count)") // => 0
let token = myStringMap.observe { changes in
    switch changes {
    case .initial(let myStringMap):
        // Will print "myStringMap.count: 1"
        print("myStringMap.count: \(myStringMap.count)")
       print("Dog Name: \(myStringMap["nameOfDog"])") // => "Rex"
        break
    case .update:
        // Will not be hit in this example
        break
    case .error:
        break
    }
}
try! realm.write {
    myStringMap["nameOfDog"] = "Rex"
}
// end of run loop execution context
```
If no key paths are given, the block will be executed on any insertion, modification, or deletion for all object properties and the properties of any nested, linked objects. If a key path or key paths are provided, then the block will be called for changes which occur only on the provided key paths. For example, if:
```
class Dog: Object {
    @Persisted var name: String
    @Persisted var age: Int
    @Persisted var toys: List<Toy>
}
// ...
let dogs = myObject.mapOfDogs
let token = dogs.observe(keyPaths: ["name"]) { changes in
    switch changes {
    case .initial(let dogs):
       // ...
    case .update:
       // This case is hit:
       // - after the token is initialized
       // - when the name property of an object in the
       // collection is modified
       // - when an element is inserted or removed
       //   from the collection.
       // This block is not triggered:
       // - when a value other than name is modified on
       //   one of the elements.
    case .error:
        // ...
    }
}
// end of run loop execution context
```
- If the observed key path were ["toys.brand"], then any insertion or deletion to the toys list on any of the collection’s elements would trigger the block. Changes to the brand value on any Toy that is linked to a Dog in this collection will trigger the block. Changes to a value other than brand on any Toy that is linked to a Dog in this collection would not trigger the block. Any insertion or removal to the Dog type collection being observed would also trigger a notification.
- If the above example observed the ["toys"] key path, then any insertion, deletion, or modification to the toys list for any element in the collection would trigger the block. Changes to any value on any Toy that is linked to a Dog in this collection would not trigger the block. Any insertion or removal to the Dog type collection being observed would still trigger a notification.
Note

Multiple notification tokens on the same object which filter for separate key paths do not filter exclusively. If one key path change is satisfied for one notification token, then all notification token blocks for that object will execute.

You must retain the returned token for as long as you want updates to be sent to the block. To stop receiving updates, call invalidate() on the token.

Warning

This method cannot be called during a write transaction, or when the containing Realm is read-only.

Note

The keyPaths parameter refers to object properties of the collection type and does not refer to particular key/value pairs within the collection.
DefaultÂ Implementation Parameters keyPaths
Only properties contained in the key paths array will trigger the block when they are modified. If nil, notifications will be delivered for any property change on the object. String key paths which do not correspond to a valid a property will throw an exception. See description above for more detail on linked properties.
queue
The serial dispatch queue to receive notification on. If nil, notifications are delivered to the current thread.
block
The block to be called whenever a change occurs.
Return Value
A token which must be held for as long as you want updates to be delivered.

Returns if this collection is frozen
Declaration
Swift
```
var isFrozen: Bool { get }
```
Returns a frozen (immutable) snapshot of this collection.

The frozen copy is an immutable collection which contains the same data as this collection currently contains, but will not update when writes are made to the containing Realm. Unlike live collections, frozen collections can be accessed from any thread.

Warning
Declaration
Swift
```
func freeze() -> Self
```
Returns a live (mutable) version of this frozen collection.

This method resolves a reference to a live copy of the same frozen collection. If called on a live collection, will return itself.
Declaration
Swift
```
func thaw() -> Self?
```

A publisher that emits Void each time the collection changes.

Despite the name, this actually emits after the collection has changed.
Declaration
Swift
```
public var objectWillChange: RealmPublishers.WillChange<Self> { get }
```
A publisher that emits the collection each time the collection changes.
A publisher that emits the collection each time the collection changes on the given property keyPaths.
A publisher that emits a collection changeset each time the collection changes.
Declaration
Swift
```
public var changesetPublisher: RealmPublishers.MapChangeset<Self> { get }
```
A publisher that emits a collection changeset each time the collection changes on the given property keyPaths.
Declaration
Swift
```
public func changesetPublisher(keyPaths: [String]?) -> RealmPublishers.MapChangeset<Self>
```

Available where Value: OptionalProtocol, Value.Wrapped: ObjectBase

Returns the minimum (lowest) value of the given property among all the objects in the collection, or nil if the collection is empty.

Warning

Only a property whose type conforms to the MinMaxType protocol can be specified.
Declaration
Swift
```
func min<T>(of keyPath: KeyPath<Value.Wrapped, T>) -> T? where T : _HasPersistedType, T.PersistedType : MinMaxType
```
Parameters keyPath
The keyPath of a property whose minimum value is desired.
Returns the maximum (highest) value of the given property among all the objects in the collection, or nil if the collection is empty.

Warning

Only a property whose type conforms to the MinMaxType protocol can be specified.
Declaration
Swift
```
func max<T>(of keyPath: KeyPath<Value.Wrapped, T>) -> T? where T : _HasPersistedType, T.PersistedType : MinMaxType
```
Parameters keyPath
The keyPath of a property whose minimum value is desired.
Returns the sum of the given property for objects in the collection, or nil if the collection is empty.

Warning

Only names of properties of a type conforming to the AddableType protocol can be used.
Declaration
Swift
```
func sum<T>(of keyPath: KeyPath<Value.Wrapped, T>) -> T where T : _HasPersistedType, T.PersistedType : AddableType
```
Parameters keyPath
The keyPath of a property conforming to AddableType to calculate sum on.
Returns the average value of a given property over all the objects in the collection, or nil if the collection is empty.

Warning

Only a property whose type conforms to the AddableType protocol can be specified.
Declaration
Swift
```
func average<T>(of keyPath: KeyPath<Value.Wrapped, T>) -> T? where T : _HasPersistedType, T.PersistedType : AddableType
```
Parameters keyPath
The keyPath of a property whose values should be summed.

Returns a Results containing the objects in the collection, but sorted.

Objects are sorted based on the values of the given key path. For example, to sort a collection of Students from youngest to oldest based on their age property, you might call students.sorted(byKeyPath: "age", ascending: true).

Warning

Collections may only be sorted by properties of boolean, Date, NSDate, single and double-precision floating point, integer, and string types.
Declaration
Swift
```
func sorted<T>(by keyPath: KeyPath<Value.Wrapped, T>, ascending: Bool) -> Results<Value> where T : _HasPersistedType, T.PersistedType : SortableType
```
Parameters keyPath
The key path to sort by.
ascending
The direction to sort in.

Returns the minimum (lowest) value of the collection, or nil if the collection is empty.
Declaration
Swift
```
func min() -> Value?
```
Returns the maximum (highest) value of the collection, or nil if the collection is empty.
Declaration
Swift
```
func max() -> Value?
```

Returns the sum of the values in the collection, or nil if the collection is empty.
Declaration
Swift
```
func sum() -> Value
```

Returns the average of all of the values in the collection.

Declaration

Swift

func average<T>() -> T? where T : _HasPersistedType, T.PersistedType : AddableType

DefaultÂ Implementation
Returns a Results containing the objects in the collection, but sorted.

Objects are sorted based on their values. For example, to sort a collection of Dates from neweset to oldest based, you might call dates.sorted(ascending: true).
Parameters ascending
The direction to sort in.

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