Hashtables and key order

Question

Is there a way to keep the order of keys in a hashtable as they were added? Like a push/pop mechanism.

Example:

$hashtable = @{}

$hashtable.Add("Switzerland", "Bern")
$hashtable.Add("Spain", "Madrid")
$hashtable.Add("Italy", "Rome")
$hashtable.Add("Germany", "Berlin")
$hashtable

I want to retain the order in which I've added the elements to the hashtable.

Answer 1

There is no built-in solution in PowerShell V1 / V2. You will want to use the .NET System.Collections.Specialized.OrderedDictionary:

$order = New-Object System.Collections.Specialized.OrderedDictionary
$order.Add("Switzerland", "Bern")
$order.Add("Spain", "Madrid")
$order.Add("Italy", "Rome")
$order.Add("Germany", "Berlin")


PS> $order

Name                           Value
----                           -----
Switzerland                    Bern
Spain                          Madrid
Italy                          Rome
Germany                        Berlin

In PowerShell V3 you can cast to [ordered]:

PS> [ordered]@{"Switzerland"="Bern"; "Spain"="Madrid"; "Italy"="Rome"; "Germany"="Berlin"}

Name                           Value
----                           -----
Switzerland                    Bern
Spain                          Madrid
Italy                          Rome
Germany                        Berlin