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Java Forum / General / August 2007Copying collection without duplicates
Hello! I have the following method overriding Collection.addAll: @Override public boolean addAll(int index, Collection<? extends E> cln) { if ( containsAll(cln) ) { return false; } //build list without dupes (always) ArrayList<E> al = new ArrayList<E>(cln.size()); Iterator<? extends E> itr = cln.iterator(); while ( itr.hasNext() ) { E elem = itr.next(); if ( !contains(elem) ) { al.add(elem); } } cln = al; //allows dupes and nulls return super.addAll(index, cln); } Is there any faster way without overriding other methods? Karsten >Is there any faster way without overriding other methods? To dedup, sort and then compare elt with prev, in one pass. You can then use Iterator.remove or copy non-dups to a new List. see http://mindprod.com/products2.html#SORTED for sample code.  SignatureRoedy Green Canadian Mind Products The Java Glossary http://mindprod.com > Hello! > [quoted text clipped - 33 lines] > > Karsten Yep! Set<?> uniqueCollection = new TreeSet(collection); > > Hello! > [quoted text clipped - 37 lines] > > Set<?> uniqueCollection = new TreeSet(collection); Hmm how does this skip duplicates? Karsten >>> Hello! >>> I have the following method overriding Collection.addAll: [quoted text clipped - 27 lines] > > Hmm how does this skip duplicates? A set contains no duplicates, so if the collection were the list "A", "B", "A" the treeset would contain "A", "B". However, the TreeSet iterator is in compareTo order, not the List order. If the collection is too large for linear scanning, I would implement the no-duplicates list using two data structures, a HashSet for determining which elements are eligible for adding, and a List to preserve order. Patricia >>>> Is there any faster way without overriding other methods? >>>> Karsten [quoted text clipped - 6 lines] > "B", "A" the treeset would contain "A", "B". However, the TreeSet > iterator is in compareTo order, not the List order. A LinkedHashSet may be preferable if preserving the order is important: http://java.sun.com/j2se/1.5.0/docs/api/java/util/LinkedHashSet.html Dan. SignatureDaniel Dyer http//www.uncommons.org >>>>> Is there any faster way without overriding other methods? >>>>> Karsten [quoted text clipped - 10 lines] > > http://java.sun.com/j2se/1.5.0/docs/api/java/util/LinkedHashSet.html I don't think LinkedHashSet has the ability to addAll at a specified index. The following is a quote from the original article: > I have the following method overriding Collection.addAll: > > @Override > public boolean addAll(int index, Collection<? extends E> cln) > { Collection does not have a two argument addAll. List does, so I suspect the new class is supposed to implement List. Patricia > >>>>> Is there any faster way without overriding other methods? > >>>>> Karsten [quoted text clipped - 24 lines] > > Patricia Very nice Patricia, I also found this on commons-collections http://commons.apache.org/collections/api-release/org/apache/commons/collections /set/ListOrderedSet.html Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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