SC2Mapster

Write your own function:

Get Players Controlled By
    Options: Function
    Return Type: Player Group
    Parameters
        Player Group = (All players) <Player Group>
        Controller = Computer <Player Controller>
    Grammar Text: Get Players Controlled By(Player Group, Controller)
    Hint Text: (None)
    Custom Script Code
    Local Variables
        tmp pg = (Empty player group) <Player Group>
    Actions
        Player Group - Pick each player in Player Group and do (Actions)
            Actions
                General - If (Conditions) then do (Actions) else do (Actions)
                    If
                        (Controller of player (Picked player)) == Controller
                    Then
                        Player Group - Add player (Picked player) to tmp pg
                    Else
        General - Return tmp pg

This function can then be used in all your player-loops:

Player Group - Pick every player in (Get Players Controlled By((All Players), Computer) and do (Actions)