CODEWITHSUNDEEP
arrayspowershellpropertiespscustomobject
FatalMerlin
FatalMerlin

Reputation: 1540

How to add a custom property to a PowerShell array?

Say I have a PowerShell array $Sessions = @() which I am going to fill with PSCustomObjects. How can I add a custom property to the array itself? E.g. so I can have $Sessions.Count which is built-in and $Sessions.Active which I want to set to the active session count.

I know that I can add properties to PSCustomObjects (in a dirty way) with

$MyCustomObject = "" | Select-Object Machine, UserName, SessionTime

but though doing so on an array would not result in the property being added.

So how can I achieve my goal? Is there any way to create a custom array?

Upvotes: 8

Views: 28108

Answers (2)

Mathias R. Jessen
Mathias R. Jessen

Reputation: 174545

As Matt commented, you can use the Add-Member on an enumerable type by supplying it as a positional argument to the -InputObject parameter.

To allow for resizing after adding the new property, use a generic List instead of @():

$list = [System.Collections.Generic.List[psobject]]::new()
$list.AddRange(@(
  [pscustomobject]@{SessionId = 1; Active = $true}
  [pscustomobject]@{SessionId = 2; Active = $false}
  [pscustomobject]@{SessionId = 3; Active = $true}
) -as [psobject[]])

Add-Member -InputObject $list -MemberType ScriptProperty -Name ActiveSessionCount -Value {
  return @($this |? Active -eq $true).Count
}

Now you can retrieve the active session count easily:

PS C:\> $list.ActiveSessionCount
2

Upvotes: 3

Matt
Matt

Reputation: 46710

The answer to your question as stated would be to just use Add-Member on the array object.

Add-Member -InputObject $sessions -MemberType NoteProperty -Name "State" -Value "Fabulous"

Adding a property to each element after you created the object is similar.

$sessions | ForEach-Object{
    $_ | Add-Member -MemberType NoteProperty -Name "State" -Value "Fabulous"
}

This of course comes with a warning (that I forgot about). From comments

Beware, though, that appending to that array ($sessions += ...) will replace the array, thus removing the additional property.

Ansgar Wiechers

Depending on your use case there are other options to get you want you want. You can save array elements into distinct variables:

# Check the current object state
$state = $object.Property .....

# Add to the appropriate array.
if($state -eq "Active"){
    $activeSessions += $object
} else {
    $inactiveSessions += $object
}

Or you could still store your state property and post process with Where-Object as required:

# Process each inactive session
$sessions | Where-Object{$_.State -eq "Active"} | ForEach-Object{}

To avoid the destroying / recreating array issue, which can be a performance hog, you could also use an array list instead.

$myArray = New-Object System.Collections.ArrayList
Add-Member -InputObject $myArray -MemberType ScriptMethod -Name "NeverTellMeTheOdds" -Value {
    $this | Where-Object{$_ % 2 -ne 0}
}

$myArray.AddRange(1..10)
$myArray.NeverTellMeTheOdds()

Notice that the array had its member added then we added its elements.

Upvotes: 16

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