function RandomEnum takes nothing returns nothing
  set UNITS[UNITS_COUNT] = GetEnumUnit()
  set UNITS_COUNT = UNITS_COUNT+1
endfunction

function RandomUnit takes group g returns unit u
  set UNITS_COUNT = 0
  call ForGroup(g, function RandomEnum)
  if(UNITS_COUNT == 0) then
   return null
  endif
  return UNITS[GetRandomInt(0, UNITS_COUNT)]
endfunction

globals
       constant group udg_G = CreateGroup()
       unit RandomUnit_u
       integer RandomUnit_i
endglobals

function RandomUnit_filter takes nothing returns boolean
       local unit u = GetFilterUnit()
       if true then //Условие отбора
           set RandomUnit_i = RandomUnit_i + 1
           if GetRandomInt(1, RandomUnit_i) == 1 then
               set RandomUnit_u = u
           endif
           set u = null
           return true
       endif
       set u = null
       return false
endfunction

function Example takes nothing returns nothing
       set RandomUnit_i = 0
       set RandomUnit_u = null
       call GroupEnumUnitsInRect(udg_G, bj_mapInitialPlayableArea, Filter(function RandomUnit_filter))
       //Действия с RandomUnit_u
endfunction