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.