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    copied!<p>I assume you can use additional libraries, this solution is based on that. Pull in <a href="https://code.google.com/p/guava-libraries/" rel="nofollow">Guava</a> and make use of a <a href="http://guava-libraries.googlecode.com/svn/tags/release03/javadoc/com/google/common/collect/Multimap.html" rel="nofollow"><code>MultiMap</code></a>:</p> <pre><code>LinkedListMultimap&lt;String, String&gt; mappedPersons = LinkedListMultimap.create(); for (int i = 0; i &lt; IDArray.size(); i++) { IdenPerson person = IDArray.get(i); mappedPersons.put(person.name, person.dis); } List&lt;IdenPerson&gt; uniques = new ArrayList&lt;IdenPerson&gt;(mappedPersons.size()); for(int i = 0 ; i &lt; IDArray.size(); i++) { if(mappedPersons.get(IDArray.get(i).name).size() == 1) { uniques.add(IDArray.get(i)); } } </code></pre> <p>Code needs cleanup, and can be optimized, but you get the gist.</p> <p>On a side note, you should definitely follow better naming standards and use proper accessor/mutators for your Java objects.</p> <p><em>New side note: next time, please indicate if the question is related to an assignment or homework. Giving near complete solutions in such cases does not help you in the long run</em></p> <hr> <p>If you cannot pull in other libraries for any reason, you can accomplish the task in the same way, by replacing the multimap with a map/list combo:</p> <pre><code>Map&lt;String, Set&lt;String&gt;&gt; mappedPersons = new HashMap&lt;String, Set&lt;String&gt;&gt;(IDArray.size()); for (int i = 0; i &lt; IDArray.size(); i++) { IdenPerson person = IDArray.get(i); List&lt;String&gt; diseases = mappedPersons.get(person.name); if(diseases == null) { diseases = new HashSet&lt;String&gt;(4); mappedPersons.put(person.name, diseases); } diseases.add(person.dis); } List&lt;IdenPerson&gt; uniques = new ArrayList&lt;IdenPerson&gt;(mappedPersons.size()); for(int i = 0 ; i &lt; IDArray.size(); i++) { if(mappedPersons.get(IDArray.get(i).name).size() == 1) { uniques.add(IDArray.get(i)); } } </code></pre>
 

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