Removing Empty Array Elements (Part 1)

by Feb 6, 2019

Occasionally you come across lists (arrays) with empty elements. What’s the best way of removing empty elements?

Let’s first focus on a common use case: the code below creates a software inventory by reading the installed software from the registry. The software list is then displayed in a grid view window, and most likely you’ll see elements with empty properties:

$Paths = 'HKCU:\Software\Microsoft\Windows\CurrentVersion\Uninstall\*',
    'HKLM:\Software\Microsoft\Windows\CurrentVersion\Uninstall\*',
    'HKLM:\SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Uninstall\*',
    'HKCU:\SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Uninstall\*'

$software = Get-ItemProperty -Path $paths -ErrorAction Ignore |
  Select-Object -Property DisplayName, DisplayVersion, UninstallString

$software | Out-GridView 

Let’s eliminate all entries with an empty DisplayName:

# remove elements with empty DisplayName property
$software = $software | Where-Object { [string]::IsNullOrWhiteSpace($_.DisplayName)}

Since empty properties can either be “really” empty ($null) or contain an empty string (‘’), you have to check both. A much easier way is using an implicit conversion to Boolea. However, in this case a value of 0 will also be removed:

# remove elements with empty DisplayName property
$software = $software | Where-Object { $_.DisplayName }

Using the simplified syntax introduced in PowerShell 3, you could even write:

# remove elements with empty DisplayName property
$software = $software | Where-Object DisplayName

And if you’d like to save a couple of milliseconds, use the where method instead:

# remove elements with empty DisplayName property
$software = $software.Where{ $_.DisplayName }

If you are dealing with really large arrays, a foreach loop is way more efficient (about 15x faster):

# remove elements with empty DisplayName property
$software = foreach ($_ in $software){ if($_.DisplayName) { $_ }}

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