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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