compute the wight of each tag for each item in matlab

I have an array like below:

<table style="width:10%">
  <tr>
    <td>Item</td>
    <td>Tag</td> 
  </tr>
  <tr>
    <td>1</td>
    <td>2</td> 
  </tr>
  <tr>
    <td>1</td>
    <td>3</td> 
  </tr>
  <tr>
    <td>2</td>
    <td>1</td> 
  </tr>
  <tr>
    <td>3</td>
    <td>2</td> 
  </tr>
  <tr>
    <td>3</td>
    <td>2</td> 
  </tr>
  <tr>
    <td>3</td>
    <td>4</td> 
  </tr>
</table>

I want to compute the weight of each tag for each item in array. for example the wight of tag 2 for item 3 is 0.66, while the wight of tag 2 for item 1 is 0.5. Is there a simple way in matlab to do this?

via Chebli Mohamed