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Some short PowerShell tips #2

Tip 3: 

Are you using Where-Object or if/else/elseif in a loop to filter out or to process whatever you need? Consider using: Group-Object.​ 
PS H:\> Get-Help Group-Object

NAME
    Group-Object

SYNTAX
    Group-Object [[-Property] <Object[]>] [-NoElement] [-AsHashTable] [-AsString] [-InputObject <psobject>] [-Culture <
    string>] [-CaseSensitive]  [<CommonParameters>]


ALIASES
    group 

That does Group-Object do? It groups ​your array of objects together based on the same value on a property in that array. It does it very efficient and also very fast: https://docs.microsoft.com/en-us/powershell/module/microsoft.powershell.utility/group-object?view=powershell-6

For example, I want to run some actions against my PoweredOn VMs and some other actions on my PoweredOff VMs. I can group them together based on power state and run actions on it. To make it simple, I group them and only care for the amount of VMs:

PS C:\> $AllVMsGrouped = Get-VM | Group-Object -Property "PowerState"
PS C:\> $AllVMsGrouped

Count Name                      Group
----- ----                      -----
  118 PoweredOff                {…}
10441 PoweredOn                 {…}

PS C:\> 

By default, the Group-Object returns a table with the count of objects in a group, the unique name and the group (all the objects in that group). And I have the results! Now I can loop through the group, or pipe the whole group to another cmdlet.

When working with a large dataset the speed difference can be significant. Here is a script that does the same and measures the time it takes to process the different methods. Group-Object is by far the fastest.

# Connect to (all) your vCenter servers here

$TimesToRun = 5             # Select how many times to run the test
$SecondsBetweenTests = 20   # Select how long to wait before starting the next test

$IfTimeResults = @()
$WhereTimeResults = @()
$GroupingTimeResults = @()
$AdvGroupingTimeResults = @()

# Loop through TimesToRun
for ($i = 1; $i -lt $TimesToRun + 1; $i++) {
    Write-Host "Running test $($i)..."

    $VMs = Get-VM                           # Every run ensures fresh data to prevent caching

    Start-Sleep $SecondsBetweenTests        # This prevents starting the measurement before the previous command finishes
    
    # The if method
    $IfTime = Measure-Command {
        $PoweredOff = 0
        $PoweredOn = 0
        foreach ($VM in $VMs) {
            if ($VM.PowerState -eq 0) {$PoweredOff += 1}
            if ($VM.PowerState -eq 1) {$PoweredOn += 1}
        }
        write-host "PoweredOff: $($PoweredOff)"
        write-host "PoweredOn: $($PoweredOn)"
    }
    $IfTimeResults += $IfTime
    
    Start-Sleep $SecondsBetweenTests
    
    # The Where-Object method
    $WhereTime = Measure-Command {
        write-host "PoweredOff: $(($VMs | Where-Object{$_.PowerState -eq 'PoweredOff'}).count)"
        write-host "PoweredOn: $(($VMs | Where-Object{$_.PowerState -eq 'PoweredOn'}).count)"
    }
    $WhereTimeResults += $WhereTime
    
    Start-Sleep $SecondsBetweenTests
    
    # The Group-Object method
    $GroupingTime = Measure-Command {
        $VMsGrouped = $VMs | Group-Object -Property "PowerState"
        write-host "PoweredOff: $(($VMsGrouped | Where-Object {$_.Name -eq 'PoweredOff'}).Count)"
        write-host "PoweredOn: $(($VMsGrouped | Where-Object {$_.Name -eq 'PoweredOn'}).Count)"
    }
    $GroupingTimeResults += $GroupingTime
    
    Start-Sleep $SecondsBetweenTests
    
    # Another Group-Object method
    $AdvGroupingTime = Measure-Command {
        $AdvVMsGrouped = $VMs | Group-Object -Property "PowerState" -AsHashTable -AsString
        write-host "PoweredOff: $(($AdvVMsGrouped.PoweredOff).Count)"
        write-host "PoweredOn: $(($AdvVMsGrouped.PoweredOn).Count)"
    }
    $AdvGroupingTimeResults += $AdvGroupingTime
}

# Write the result of the tests
Write-Host "IfTimeResults: $([math]::Round(($IfTimeResults | Measure-Object -Average -Property TotalMilliseconds).Average,1))"
Write-Host "WhereTimeResults: $([math]::Round(($WhereTimeResults | Measure-Object -Average -Property TotalMilliseconds).Average,1))"
Write-Host "GroupingTimeResults: $([math]::Round(($GroupingTimeResults | Measure-Object -Average -Property TotalMilliseconds).Average,1))"
Write-Host "AdvGroupingTimeResults: $([math]::Round(($AdvGroupingTimeResults | Measure-Object -Average -Property TotalMilliseconds).Average,1))" 
🤓
 
🤓
1
PS H:\> $AdvVMsGrouped = $VMs | Group-Object -Property "PowerState" -AsHashTable
PS H:\> $AdvVMsGrouped.GetEnumerator().Name | Get-Member


   TypeName: VMware.VimAutomation.ViCore.Types.V1.Inventory.PowerState
   

PS H:\> $AdvVMsGrouped = $VMs | Group-Object -Property "PowerState" -AsHashTable -AsString
PS H:\> $AdvVMsGrouped.GetEnumerator().Name | Get-Member


   TypeName: System.String 

And now time for the results. I ran mine against an enterprise environment with 8 vCenters, so lot's of VMs. The results are all in milliseconds:

 
 

While all give the same results, the last one is the fastest!!!


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Tuesday, 28 November 2023