comparison of attribute values

Hi,
What I would like to do is to insert a row into a table if there is a
difference in an attribute value anywhere in the document; for example, this
data should produce 2 columns (USD and EUR):

<fees>
    <basic-fees>
        <fee1 currency="USD"><amount>20</amount></fee1>
        <fee2 currency="EUR"><amount>25</amount></fee2>
    </basic-fees>
    <special-fees>
        <fee3 currency="EUR"><amount>20</amount></fee3>
    </special-fees>
    <total currency="USD">65</total>
</fees>

<!-- desired output for above doc -->
<table>
    <tr><td>FEE</td><td>USD</td><td>EUR</td></tr>
    <tr><td>fee1</td><td> 20   </td><td>        </td></tr>
    <tr><td>fee2 </td><td>        </td><td> 25  </td></tr>
    <tr><td>fee3</td><td>        </td><td>  20  </td> </tr>
    <tr><td>total</td><td> 65   </td><td>       </td></tr>
</table>

but if there is only one currency used throughout the document, it should
only create one column (e.g., USD).

<fees>
    <basic-fees>
        <fee1 currency="USD"><amount>20</amount></fee1>
        <fee2 currency="USD"><amount>25</amount></fee2>
    </basic-fees>
    <special-fees>
        <fee3 currency="USD"><amount>20</amount></fee3>
    </special-fees>
    <total currency="USD">65</total>
</fees>

<!-- desired output for above doc -->
<table>
    <tr><td> FEE </td><td>USD</td></tr>
    <tr><td>fee1</td><td> 20   </td></tr>
    <tr><td>fee2 </td><td> 25  </td></tr>
    <tr><td>fee3</td><td>  20  </td> </tr>
    <tr><td>total</td><td> 65   </td> </tr>
</table>


 I have a feeling that I'm overlooking something painfully obvious, but any
help would be greatly appreciated.

TIA,
John


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