line numbers for all subsequent records after the first one for the same position should be in the format of <Pos No>.<Incremental No

When multiple records are encounteredin transaction,  the line numbers for all subsequent records after the first one for the same position should be in the format of <Pos No>.<Incremental No>

xml sample file:
<orderRequest>
   <lineRequest>
      <LineNumber>1</LineNumber>
       ….
       ….
    </lineRequest>
   
    <lineRequest>
      <LineNumber>2</LineNumber>
       ….
       ….
    </lineRequest>
   
    <lineRequest>
      <LineNumber>3</LineNumber>
       ….
       ….
    </lineRequest>

</OrderRequest>

Here the second lineRequest should have the lineNumber as 1.1 instead of 2.

Kndly let me know, how to do it in maps?

Thanks inadvance.