SortedList Class

I think many people are looking for a class key/value pair that maintains the order in which the elements are inserted.

Can anyone leads us there?

Thank you!

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What you're looking may be the Dictionary class.

System.Collections.Generic.Dictionary

However, the documentation there states that the results are returned in an "undefined" order. So your best bet may be to maintain a list of keys in insertion order and a separate SortedList or Dictionary with the same keys. Wrap the whole thing in a custom class that inherits SortedList, and override the Add and Remove methods to update your un-sorted key list.

Doesn't say, would be helpful if it did...

• It does say that keys must be unique.

Actually it does say "a SortedList does not allow duplicate keys".
Any suggestions for a class that does allow duplicates?

I don't think you can do that... if you need to store multiple items with the same key, what you need is to create a SortedList with another container type as the value. You then add your values to the container class.

For example: SortedList<string, List<x>> could do the job. You'd need to create a wrapper for this by creating a new class that inherits this, like this:

class MultiList : SortedList <string, List<x>> {

  // create a custom add method to add multiple values for one key
  override void Add(string key, x value) {
    if(keys.Contains(string)) {
      this[key].add(value);
    else {
      List<x> l=new List<x>();
      l.Add(value);
      this.add(key, l);
    }
  }
}

Using this technique, adds are the same as you're used to with SortedList, but since the list is actually storing lists, rather than individual items, you need to index the result to get the specific item you need. This should give you the first item in the result (I haven't tried this... if it's wrong, please edit this to correct it):

result = MyMultiList[key][0];

you can also iterate through the contents of a single key's values, like so:

foreach(x item in MyMultiList[key]) {

To answer OxG's question above, the answer is that keys in a sorted list must be unique. Thus trying to call the Add() method with a non-unique key will generate an exception, as shown in the following PowerShell session log:

PSH [C:\foo]: $sl = New-Object system.Collections.SortedList
PSH [C:\foo]: $sl
PSH [C:\foo]: $sl.Add("first","foo")
PSH [C:\foo]: $sl

Name                           Value
----                           -----
first                          foo

  
PSH [C:\foo]: $sl.Add("first","foo2")
Exception calling "Add" with "2" argument(s): "Item has already been added. Key in dictionary: 'first'  Key being added: 'first'"
At line:1 char:8
+ $sl.Add <<<< ("first","foo2")
    + CategoryInfo          : NotSpecified: (:) [], MethodInvocationException
    + FullyQualifiedErrorId : DotNetMethodException

This example has some data and get enumerator from their values,keys shown below.

SortedList sl = new SortedList();

sl.Add("hip", "hop");
sl.Add("fest", "country");
sl.Add("quer", "bolete");

if ( x.Contains("hip") )
Console.Write("Hip has gone!");

IDictionaryEnumerator iDic = x.GetEnumerator();

while ( iDic.MoveNext() )
Console.Write("key:" + iDic.Key.ToString() + " value:" + iDic.Value.ToString());

The example already has the sample data entered in alphabetical order as shown below:

SortedList mySL = new SortedList();
mySL.Add("First", "Hello");
mySL.Add("Second", "World");
mySL.Add("Third", "!");

It would be less confusing and a better demonstration to change the order.

# get-sortedlist.ps1
# Sortedlist sample using PowerShell
# Thomas Lee - tfl@psp.co.uk

# Define helper function

function PrintKeysAndValues( $myList )  {
"`t-KEY-`t-VALUE-" 
for ( [int] $i = 0; $i -lt $myList.Count; $i++ )  {
    "`t{0}:`t{1}" -F $myList.GetKey($i), $myList.GetByIndex($i)
      }
""
}

# Create and initialise a new SortedList object
$mySL = new-object system.collections.SortedList
$mySL.Add("First", "Hello")
$mySL.Add("Second", "World")
$mySL.Add("Third", "!")

# Display the properties and values of the SortedList
"`$mySL" 
"  Count:    {0}" -f $mySL.Count
"  Capacity: {0}" -f $mySL.Capacity
"  Keys and Values:"
PrintKeysAndValues( $mySL )

# Add two more and display results
$mysl.add("aaaa",  "aaaa")
$mysl.add("zzzz" , "zzzz")

# display results
"`$mySL after two additions" 
"  Count:    {0}" -f $mySL.Count
"  Capacity: {0}" -f $mySL.Capacity
"  Keys and Values:"
PrintKeysAndValues( $mySL )

This script produces the following output

PS D:\foo> 
D:\foo\get-sortedlist.ps1
$mySL
  Count:    3
  Capacity: 16
  Keys and Values:
 -KEY- -VALUE-
 First: Hello
 Second: World
 Third: !

$mySL after two additions
  Count:    5
  Capacity: 16
  Keys and Values:
 -KEY- -VALUE-
 aaaa: aaaa
 First: Hello
 Second: World
 Third: !
 zzzz: zzzz