$groups = ps | group Name

$groups | Sort-Object Name | % {
    $g = $_.Group | measure PM -Sum;
    New-Object psobject -Property @{ Name2 = $_.Name; Count = $g.Count; Sum = $g.Sum }
}

$groups = ps | group Name

$groups | Sort-Object Name | % {
    $g = $_.Group | measure PM -Sum;
    select -Property @{ Name = 'Name'; expression = { $_.Name }},
                     @{ Name = 'Count'; expression = { $g.Count }},
                     @{ Name = 'Sum'; expression = { $g.Sum }}
}