Fastest Way to Return Names in array1 that are not in array2

PowerShell Help
1

What is the fastest way to return elements in array1 not found in array2?

Array1 has like 5000 entries
Array2 has like 18000 entries
Each Array only has 1 value and its name, so not able to use hash keypairs.
Arrays are not sorted

Provide simple example of best option you recommend.

2

Compare-Object. See help for examples.

3

what he said :slight_smile:

$Array1 = 1..5000 | % { [PSCustomObject]@{
        bla1 = $_
        bla2 = "Text$_"
    }
}

$Array2 = 3000..20000 | % { [PSCustomObject]@{
        bla1 = $_
        bla2 = "Text$_"
    }
}

# Elements in Array1 not in Array2 ==> 1 - 2999

$Duration = Measure-Command {
    $myOutput = Compare-Object -ReferenceObject $Array1 -DifferenceObject $Array2 -PassThru -Property bla1 | 
        Where-Object { $_.SideIndicator -eq '<=' }
}
'Test 1: Compare-Object and Where-Object'
"    Identified $($myOutput.count) records in $($Duration.TotalSeconds) seconds"

$Duration = Measure-Command {
    $myOutput = (Compare-Object -ReferenceObject $Array1 -DifferenceObject $Array2 -PassThru -Property bla1).Where{ $_.SideIndicator -eq '<=' } 
}
'Test 2: Compare-Object and Where() method'
"    Identified $($myOutput.count) records in $($Duration.TotalSeconds) seconds"

$Duration = Measure-Command {
    $myOutput = $Array1 | % {
        if ($_.bla1 -notin $Array2.bla1 ) { $_ }
    } 
}
'Test 3: Enumerate Array1 elements, test each against Array2'
"    Identified $($myOutput.count) records in $($Duration.TotalSeconds) seconds"

Test 1: Compare-Object and Where-Object
    Identified 2999 records in 11.8748938 seconds
Test 2: Compare-Object and Where() method
    Identified 2999 records in 10.6478435 seconds
Test 3: Enumerate Array1 elements, test each against Array2
    Identified 2999 records in 48.2678471 seconds
4

Thanks for the quick responses. I’ve tried some of these options, but still very slow. I will measure it and report my results and code examples. Also, I can’t use hash table as my 2 arrays only have 1 property in them, therefore can’t meet keypair option requirements for hashtable.

5

Tried doing CompareObject on 2 results and it works good.

However, I this error about null, but I don’t see whats wrong. The arrays are not null. If I run the contents in Reference Object it works fine, same if I do it for DifferenceObject. After much troubleshooting, found that in my arrays there was 2 null lines, and apparently Compare-Object doesn’t work ANY null entries.

Code to replace the null entries used:
$ruleApplications = $ruleApplications -replace “^$”, “null”

Thanks for ALL of the help, much appreciated.

6

if you do not have duplicates in array why you can’t use hashtables ?
what stop you from use $hash[$key] = 1 and $hash.ContainsKey($key) ?
and even there is a duplicates you can have a $hash[$key] = $count

also there is a HashSet
https://msdn.microsoft.com/en-us/library/bb359438(v=vs.110).aspx