Visual Basic/Collections

Collection class provides an array-like container more flexible than an array in some ways and less flexible in other ways. More flexible in some ways than Collection is Dictionary class. Creating a new collection: Dim Cats As Collection Set Cats = New Collection Dimensioning and creating a new collection in one line: Dim Cats As New Collection Adding an item: Cats.Add "Item" Cats.Add "Item", "Key" ... Accessing an item at an index, in a read-only way: Cats (3) 'The third member of the collection Cats.Item(3) 'An alternative Cats.Item("Key 3") 'Works if an item has a key associated Overwriting a item at an index: NewValue = MyCollection(i) + 1 MyCollection.Add NewValue, Before:=i MyCollection.Remove Index:=i + 1 Removing an item: Collection.Remove Index Collection.Remove HashKey The size of a collection: Cats.Count Iterating over a collection, read-only: For Each Cat In Cats Rem Do something on Cat Next Iterating over a collection, read-write: 'Fill the collection Set MyCollection = New Collection For i = 1 To 10 MyCollection.Add i Next 'Increment each item by 1 For i = 1 To MyCollection.Count NewValue = MyCollection(i) + 1 MyCollection.Add NewValue, Before:=i MyCollection.Remove Index:=i + 1 Next Testing the emptiness of a collection: If Cats.Count=0 Then '... End If Testing the presence of an element in a collection: MatchFound = False For Each Member In MyCollection If Member = "SoughtValue" Then MatchFound = True Exit For End If Next Appending one collection to another: For Each Member In AppendedCollection ExtendedCollection.Add Member Next Converting a collection to an array: Dim MyArray ReDim MyArray(MyCollection.Count - 1) Index = 0 For Each Member In MyCollection MyArray(Index) = Member Index = Index + 1 Next Using a collection as a queue: Set Queue = New Collection For i = 1 To 10 Queue.Add i Next For i = 1 To 5 Queue.Remove 1 'Remove from the queue Next Using a collection as a stack: Set Stack = New Collection For i = 1 To 10 Stack.Add i Next For i = 1 To 5 Stack.Remove Stack.Count 'Remove from the stack Next Using a collection as a set: ' Using the key of a collection item will do the trick. ' The key has to be a string, hence "Str(i)" below. ' Note that Str(1) is " 1", with a leading space. Set NumberSet = New Collection For i = 1 To 10 NumberSet.Add i, Str(i) 'Value, Key Next For i = 5 To 15 'Add while catching errors resulting from existence of the key On Error Resume Next NumberSet.Add i, Str(i) 'Value, Key On Error GoTo 0 'End If Next For i = 14 To 16 'Remove On Error Resume Next 'Catch error if element not present NumberSet.Remove Str(i) On Error GoTo 0 Next 'Membership test On Error Resume Next NumberSet.Item(Str(50)) IsMember=Err.Number=0 On Error GoTo 0 ' Set NumberSet2 = New Collection For i = 10 To 25 NumberSet2.Add i, Str(i) Next 'Union Set SetUnion = New Collection For Each Item In NumberSet SetUnion.Add Item, Str(Item) 'Value, Key Next For Each Item In NumberSet2 On Error Resume Next SetUnion.Add Item, Str(Item) 'Value, Key On Error GoTo 0 Next 'Intersection Set SetIntersection = New Collection For Each Item In NumberSet On Error Resume Next Dummy = NumberSet2(Str(Item)) If Err.Number = 0 Then SetIntersection.Add Item, Str(Item) 'Value, Key End If On Error GoTo 0 Next 'Set difference Set SetDifference = New Collection For Each Item In NumberSet On Error Resume Next Dummy = NumberSet2(Str(Item)) If Err.Number <> 0 Then SetDifference.Add Item, Str(Item) 'Value, Key End If On Error GoTo 0 Next