Grouping elements

Hi  people . I've been working with grouped elements and I'm having
problems with a kind of operation. Well, I'm trying to group just the
elements with more of one occurence, to the others elements that
appears just one time, there's no need to display.    Until now I
ain't have any success, Is There anyone to help me ?        I simplify
it this way:  If I ha
<cars> 
 <car>
		<model>J980384</model>
		<name>Ranger</name>
                <categ>Pick-up</categ>
                <color>blue</color>
                <stock>6</stock>
  </car>
   <car>
		<model>V667320</model>
		<name>Sportage</name>
                <categ>sport</categ>
                <color>green</color>
                <stock>8</stock>

   </car>
   <car>
		<model>M382932</model>
		<name>Silverado</name>
               <categ>pick-up</categ>
                <color>blue</color>
                <stock>3</stock>
 </car>
 <car>
		<model>L930389</model>
		<name>Jaguar</name>
                <categ>Sport</categ>
                <color>red</color>
                <stock>2</stock>
  </car>
  <car>
		<model>J980384</model>
		<name>Ranger</name>
                <categ>Pick-up</categ>
                <color>grey</color>
                <stock>3</stock>
  </car>
 <car>
		<model>L930389</model>
		<name>Jaguar</name>
                <categ>Sport</categ>
                <color>blue</color>
                <stock>1</stock>
  </car>
  <car>
		<model>J980384</model>
		<name>Ranger</name>
                <categ>Pick-up</categ>
                <color>black</color>
                <stock>5</stock>
  </car>
</cars>

I Think  through this example you'll understand what I want to do.  

My question: I have Two categories: Supposing that my structure have
more than 100 models, I need  to group only those have more of one
representation. How I'm selecting by the model number, in this example
 I wish that the grouped elements   appear this way


Car:   L930389  Jaguar  Sport
 occurence : 2
      
              Total stock: 3


Car:   L930384  Ranger  Pick-up
 occurence : 3

              Total stock: 14

The elements with one occurence shouldn't be showed

Thanks .


  Marcos Hercules dos Santos