Remove duplicate affiliation

Hi Friends,

We need to remove duplicate affiliation that can be unique by @xreflabel.
Could you please let me know any clue.

Input

<authorgroup>

<author>

<name>a</name>

<affiliation xreflabel="1"><org>..</org> First affiliation</affiliation>

<affiliation xreflabel="2"><sup>..</sup> Second affiliation</affiliation>

</author>

<author>

<name>b</name>

<affiliation xreflabel="1"><org>..</org> First affiliation</affiliation>

</author>

<author>

<name>c</name>

<affiliation xreflabel="3"><org>..</org> Third affiliation</affiliation>

</author>

<author>

<name>d</name>

<affiliation xreflabel="1"><org>..</org> First affiliation</affiliation>

<affiliation xreflabel="4"><sub>..</sub> Forth affiliation</affiliation>

</author>

 

Output

<aug>

<au>a</au>

<au>b</au>

<au>c</au>

<au>d</au>

<aff><org>.</org> First affiliation</aff>

<aff><sup>.</sup> Second affiliation</aff>

<aff><org>.</org> Third affiliation</aff>

<aff><sub>.</sub> Forth affiliation</aff>