SortedListUse the SortedList collection to store keys and values, sorted on the keys.
SortedList. Some collections keep their element sorted as you use them. The SortedList type, for example, always sorts its keys. We add keys and values to SortedList.
Unlike a List, the SortedList stores both keys and values. For a collection with just keys (that is more like a List, except no duplicates) consider a SortedSet.
First example. Here we create a SortedList, and then invoke Add(). In Add, the first argument is the key to add. The second argument is the value at that key.
Detail We use the For-Each loop over the SortedList. The KeyValuePair is used (with matching types to the SortedList) in the loop.
For Each, For
Tip The SortedList has no ways to reorder its elements. If you want to change the ordering, you must create a new collection.
Module Module1 Sub Main() ' Create SortedList and add Strings to it. Dim sorted As SortedList(Of String, String) = New SortedList(Of String, String) sorted.Add("dog", "red") sorted.Add("cat", "black") sorted.Add("zebra", "black and white") sorted.Add("ant", "black") ' Loop over pairs in the collection. For Each pair As KeyValuePair(Of String, String) In sorted Console.WriteLine(pair.Key + "/" + pair.Value) Next End Sub End Module
ant/black cat/black dog/red zebra/black and white
IndexOfKey. We can search for keys and values in the SortedList. To find a key, use IndexOfKey. The special value -1 is returned if the key does not exist—no exception is thrown.
Detail Use this function to find a value in the SortedList. The special value -1 is used here too to mean "missing."
Module Module1 Sub Main() Dim items = New SortedList(Of String, Integer) items.Add("bird", 20) items.Add("fish", 0) ' Display all pairs. For Each item As KeyValuePair(Of String, Integer) In items Console.WriteLine("ITEM: {0}", item) Next ' Find this key. Dim indexFish = items.IndexOfKey("fish") Console.WriteLine("INDEX OF FISH: {0}", indexFish) ' Find this value. Dim index20 = items.IndexOfValue(20) Console.WriteLine("INDEX OF 20: {0}", index20) ' If a key or value is missing, the value -1 is returned. Dim indexMissing = items.IndexOfKey("carrot") Console.WriteLine("INDEX OF CARROT: {0}", indexMissing) End Sub End Module
ITEM: [bird, 20] ITEM: [fish, 0] INDEX OF FISH: 1 INDEX OF 20: 0 INDEX OF CARROT: -1
Notes, duplicates. If we try to add a duplicate to the SortedList, an exception is thrown. We cannot call Add without first checking for the key in the List (consider IndexOfKey).
A summary. The SortedList is a sorted list of pairs. It is not used in the same way as a List, which makes it harder to apply in programs. A SortedSet is often a better choice.
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Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
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