Find items which are in array1 but NOT in array2

Question

I extracted two lists of computers from two different tools, Array1 and Array2.

Now I need to extract the ones which are in Array1, but not in Array2.

I managed to get all the matching ones by doing this:

$matchingComp = @()

foreach ($SCCMcomputer in $SCCMcomputers) {
    foreach ($eWPTcomputer in $eWPTcomputers) {
        if ($SCCMcomputer.Computername -eq $eWPTComputer.Computername) {
            $obj = New-Object PSObject
            $obj | Add-Member -MemberType NoteProperty -Name "ComputerName" -Value $SCCMcomputer.Computername
            $matchingComp +=$obj
        }
    }
}

$matchingComp | Export-Csv $inEWPT -Delimiter "," -NoTypeInformation

But I still need the ones that are in $SCCMcomputer but NOT in $eWPTcomputers...

I've found some solutions on SO with other languages (e.g. Perl) but not for PowerShell.

UPDATE

I still don't get the correct output, in Excel with this formula:

the output looks like:

means some are here, some not. The output in powershell is like this

means 0KB is emtpy.

$SCCMcomputers | Export-Csv $sccmexport -Delimiter "," -NoTypeInformation
$eWPTcomputers | Export-Csv $ewptexport -Delimiter "," -NoTypeInformation
Compare-Object -ReferenceObject $SCCMcomputers -DifferenceObject $eWPTcomputers | ?{$_.sideIndicator -eq "=>"} |select inputobject | Export-Csv $inEWPT -NoTypeInformation
Compare-Object -ReferenceObject $SCCMcomputers -DifferenceObject $eWPTcomputers | ?{$_.sideIndicator -eq "=="} |select inputobject | Export-Csv $inBoth -NoTypeInformation
Compare-Object -ReferenceObject $SCCMcomputers -DifferenceObject $eWPTcomputers | ?{$_.sideIndicator -eq "<="} |select inputobject | Export-Csv $inSCCM -NoTypeInformation

And both Column Name (or what it's called) from SCCMcomptuers/eWPTcomputers is "Computername"

Any idea what I could be doing wrong? Both computer arrays are generated from SQL and in hashtables (I think it's called): @{Computername=......}@{Computername...., something like this.

Update 2

foreach ($t in $sccmComputers) {
    $Test1 += $t.computername
}

$Test2 = @()
foreach ($t in $ewptComputers) {
    $Test2 += $t.computername
}

By removing the Header of the Hashtable and just having arrays full of strings works fantasctic..... even -Property computername did not work... :S

Answer 1

use compare-object cmdlet

Compare-Object -ReferenceObject $sccm -DifferenceObject $wpt | ?{$_.sideIndicator -eq "<="} |select inputobject

example :

$sccm=@(1,2,3)   
$wpt=@(2,4)

Compare-Object -ReferenceObject $sccm -DifferenceObject $wpt -IncludeEqual   

will output :

InputObject SideIndicator

---

      2 ==            
      4 =>            
      1 <=            
      3 <=

that means value "2" is on both objects, "1" and "3" only on "the left side" (ie the reference object), while "4" is only on the difference object