• Generate arrays via foreach instead of += which recreates the entire array each time
• Declare arrays using simplified syntax: just a list of comma-separated elements

$dev = $a, $b, $c, $d $test = $b, $d, $e, $f $prod = $c, $d, $f, $g $result = @( foreach ($_ in $dev) { Add-Member 'DEV' 'Y' -InputObject $_ -PassThru } foreach ($_ in $test) { Add-Member 'TEST' 'Y' -InputObject $_ -PassThru } foreach ($_ in $prod) { Add-Member 'PROD' 'Y' -InputObject $_ -PassThru } ) | Group Id | ForEach { $_.Group[0] }

# help Format-Table recognize all added properties
Add-Member ([ordered]@{
    DEV = $result[0].DEV
    TEST = $result[0].TEST
    PROD = $result[0].PROD
}) -Force -InputObject $result[0]

$result | ft -auto

The second block may be generalized to process any number of input arrays:

$addedId = @{}
$result = Sort Id -input @(
    foreach ($sourceName in 'DEV', 'TEST', 'PROD') {
        $source = Get-Variable $sourceName -value
        foreach ($item in $source) {
            Add-Member $sourceName 'Y' -InputObject $item
            if (!$addedId[$item.Id]) {
                $addedId[$item.Id] = $true
                $item
            }
        }
    }
)

• Generate arrays via foreach instead of += which recreates the entire array each time
• Declare arrays using simplified syntax: just a list of comma-separated elements

$dev = $a, $b, $c, $d $test = $b, $d, $e, $f $prod = $c, $d, $f, $g $result = @( foreach ($_ in $dev) { Add-Member 'DEV' 'Y' -InputObject $_ -PassThru } foreach ($_ in $test) { Add-Member 'TEST' 'Y' -InputObject $_ -PassThru } foreach ($_ in $prod) { Add-Member 'PROD' 'Y' -InputObject $_ -PassThru } ) | Group Id | ForEach { $_.Group[0] }

# help Format-Table recognize all added properties
Add-Member ([ordered]@{
    DEV = $result[0].DEV
    TEST = $result[0].TEST
    PROD = $result[0].PROD
}) -Force -InputObject $result[0]

$result | ft -auto

While the above code is approximately 2 times faster than the original one, it's possible to make it 5 times faster in PowerShell 5 and newer by adding properties directly via .NET method so the second block would become as follows:

$addedId = @{}
$result = Sort Id -input @(
    foreach ($sourceName in 'DEV', 'TEST', 'PROD') {
        $source = Get-Variable $sourceName -value
        $prop = [PSNoteProperty]::new($sourceName, 'Y')
        foreach ($item in $source) {
            $item.PSObject.Properties.Add($prop)
            if (!$addedId[$item.Id]) {
                $addedId[$item.Id] = $true
                $item
            }
        }
    }
)