delete all but first occurence of a pattern

[Nikolaos A. Patsopoulos]

Hi all,

I've got  xml files that  each have 500 entries marked as <article> ....
</article> .in each entry there are fields <author></author>. Some articles
have non author fields and some have more than one. What I want to do is every
article to have only one such field, e.g. if an article has 3 <author>..
</author> fields the two last must be dropped, if an article has none an empty
one <author> </author> must be added. How can i do this but in every 500
articles that are included in the same xml file? (I use VI, not gvim)

Here follows some sample entries:

<article>
                <AuthorList CompleteYN="Y">
                <Author ValidYN="Y">
                    <LastName>Heinisch</LastName>
                    <ForeName>Roberto H</ForeName>
                    <Initials>RH</Initials>
                </Author>
                <Author ValidYN="Y">
                    <LastName>Zanetti</LastName>
                    <ForeName>Carlos R</ForeName>
                    <Initials>CR</Initials>
                </Author>
                <Author ValidYN="Y">
                    <LastName>Comin</LastName>
                    <ForeName>Fabiano</ForeName>
                    <Initials>F</Initials>
                </Author>
                <Author ValidYN="Y">
                    <LastName>Fernandes</LastName>
                    <ForeName>Juliano L</ForeName>
                    <Initials>JL</Initials>
                </Author>
                <Author ValidYN="Y">
                    <LastName>Ramires</LastName>
                    <ForeName>Jos&#233; A</ForeName>
                    <Initials>JA</Initials>
                </Author>
                <Author ValidYN="Y">
                    <LastName>Serrano</LastName>
                    <ForeName>Carlos V</ForeName>
                    <Initials>CV</Initials>
                    <Suffix>Jr</Suffix>
                </Author>
            </AuthorList>
</article>

<article>

</article>

<article>
   <AuthorList CompleteYN="Y">
                <Author ValidYN="Y">
                    <LastName>Saint-Remy</LastName>
                    <ForeName>Annie</ForeName>
                    <Initials>A</Initials>
                </Author>
    </AuthorList>
</article>



The above sample should be turned into this:

<article>
                <AuthorList CompleteYN="Y">
                <Author ValidYN="Y">
                    <LastName>Heinisch</LastName>
                    <ForeName>Roberto H</ForeName>
                    <Initials>RH</Initials>
                </Author>
                </AuthorList>
</article>

<article>
                   <AuthorList CompleteYN="Y">
                <Author ValidYN="Y">

                </Author>

                </AuthorList>
</article>

<article>
   <AuthorList CompleteYN="Y">
                <Author ValidYN="Y">
                    <LastName>Saint-Remy</LastName>
                    <ForeName>Annie</ForeName>
                    <Initials>A</Initials>
                </Author>
    </AuthorList>
</article>


Thanks in advance,

Nikos