xml to xml transform

Hello!

How can I transform document:
<row @fld="f1" value="v1">
<row @fld="f1" value="v2">
<row @fld="f2" value="v3">
<row @fld="f3" value="v4">

to

<f1>
<v1/>
<v2/>
</f1>
<f2>
<v3/>
</f2>
<f3>
<v4/>
</f3>

if I don't know values f1, f2, etc. in advance?

Thanks,

Shimon

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