Streaming implementation of PowerShell's Select-Object -Unique

Select-UniqueObject.ps1

&{
    1..7
    4..9
} |
    ForEach-Object -Begin {
        $Unique = @{}
    } -Process {
        if (-not $Unique.ContainsKey($_)) { 
            $Unique.Add($_, $null)
            $_
        }
    } -End {
        $Unique.Clear()
    }