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It is provided "as is" without express or implied warranty. -- --><Head><Title>unique</Title><!-- Generated by htmldoc --></HEAD><BODY TEXT="#000000" LINK="#006600" ALINK="#003300" VLINK="#7C7F87" BGCOLOR="#FFFFFF"><A HREF="/"><IMG SRC="/images/common/sgilogo_small.gif" ALT="SGI Logo" WIDTH="80" HEIGHT="72" BORDER="0"></A><P><!--end header--><BR Clear><H1>unique</H1><Table CellPadding=0 CellSpacing=0 width=100%><TR><TD Align=left><Img src = "algorithms.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD><TD Align=right><Img src = "function.gif" Alt="" WIDTH = "194" HEIGHT = "38" ></TD></TR><TR><TD Align=left VAlign=top><b>Category</b>: algorithms</TD><TD Align=right VAlign=top><b>Component type</b>: function</TD></TR></Table><h3>Prototype</h3><tt>Unique</tt> is an overloaded name; there are actually two <tt>unique</tt>functions.<pre>template <class <A href="ForwardIterator.html">ForwardIterator</A>>ForwardIterator unique(ForwardIterator first, ForwardIterator last);template <class <A href="ForwardIterator.html">ForwardIterator</A>, class <A href="BinaryPredicate.html">BinaryPredicate</A>>ForwardIterator unique(ForwardIterator first, ForwardIterator last, BinaryPredicate binary_pred);</pre> <h3>Description</h3>Every time a consecutive group of duplicate elements appears in therange <tt>[first, last)</tt>, the algorithm <tt>unique</tt> removes all but the first element. That is, <tt>unique</tt> returns an iterator<tt>new_last</tt> such that the range <tt>[first, new_last)</tt> contains notwo consecutive elements that are duplicates. <A href="#1">[1]</A>The iterators in the range <tt>[new_last, last)</tt> are all still dereferenceable, but the elements that they point to are unspecified.<tt>Unique</tt> is stable, meaning that the relative order of elements that are not removed is unchanged. <P>The reason there are two different versions of <tt>unique</tt> is that thereare two different definitions of what it means for a consecutive groupof elements to be duplicates. In the first version, the test issimple equality: the elements in a range <tt>[f, l)</tt> are duplicates if,for every iterator <tt>i</tt> in the range, either <tt>i == f</tt> or else <tt>*i == *(i-1)</tt>.In the second, the test is an arbitrary <A href="BinaryPredicate.html">Binary Predicate</A><tt>binary_pred</tt>: the elements in <tt>[f, l)</tt> are duplicates if, for every iterator <tt>i</tt> in the range, either <tt>i == f</tt> or else<tt>binary_pred(*i, *(i-1))</tt> is <tt>true</tt>. <A href="#2">[2]</A><h3>Definition</h3>Defined in the standard header <A href="algorithm">algorithm</A>, and in the nonstandardbackward-compatibility header <A href="algo.h">algo.h</A>.<h3>Requirements on types</h3>For the first version:<UL><LI><tt>ForwardIterator</tt> is a model of <A href="ForwardIterator.html">Forward Iterator</A>.<LI><tt>ForwardIterator</tt> is mutable.<LI><tt>ForwardIterator</tt>'s value type is <A href="EqualityComparable.html">Equality Comparable</A>.</UL>For the second version:<UL><LI><tt>ForwardIterator</tt> is a model of <A href="ForwardIterator.html">Forward Iterator</A>.<LI><tt>ForwardIterator</tt> is mutable.<LI><tt>BinaryPredicate</tt> is a model of <A href="BinaryPredicate.html">Binary Predicate</A>. <A href="#3">[3]</A><LI><tt>ForwardIterator</tt>'s value type is convertible to <tt>BinaryPredicate</tt>'s first argument type and to <tt>BinaryPredicate</tt>'s second argument type.</UL><h3>Preconditions</h3><UL><LI><tt>[first, last)</tt> is a valid range.</UL><h3>Complexity</h3>Linear. Exactly <tt>(last - first) - 1</tt> applications of <tt>operator==</tt>(in the case of the first version of <tt>unique</tt>) or of <tt>binary_pred</tt>(in the case of the second version).<h3>Example</h3>Remove duplicates from consecutive groups of equal <tt>int</tt>s.<pre><A href="Vector.html">vector</A><int> V;V.push_back(1);V.push_back(3);V.push_back(3);V.push_back(3);V.push_back(2);V.push_back(2);V.push_back(1);<A href="Vector.html">vector</A><int>::iterator new_end = unique(V.begin(), V.end());<A href="copy.html">copy</A>(V.begin(), new_end, <A href="ostream_iterator.html">ostream_iterator</A><int>(cout, " ")); // The output it "1 3 2 1".</pre><P>Remove all duplicates from a vector of <tt>char</tt>s, ignoring case. Firstsort the vector, then remove duplicates from consecutive groups.<pre>inline bool eq_nocase(char c1, char c2) { return tolower(c1) == tolower(c2); }inline bool lt_nocase(char c1, char c2) { return tolower(c1) < tolower(c2); }int main(){ const char init[] = "The Standard Template Library"; <A href="Vector.html">vector</A><char> V(init, init + sizeof(init)); <A href="sort.html">sort</A>(V.begin(), V.end(), lt_nocase); <A href="copy.html">copy</A>(V.begin(), V.end(), <A href="ostream_iterator.html">ostream_iterator</A><char>(cout)); cout << endl; <A href="Vector.html">vector</A><char>::iterator new_end = unique(V.begin(), V.end(), eq_nocase); <A href="copy.html">copy</A>(V.begin(), new_end, <A href="ostream_iterator.html">ostream_iterator</A><char>(cout)); cout << endl;}// The output is:// aaaabddeeehiLlmnprrrStTtTy// abdehiLmnprSty</pre><h3>Notes</h3><P><A name="1">[1]</A>Note that the meaning of "removal" is somewhat subtle. <tt>Unique</tt>,like <tt><A href="remove.html">remove</A></tt>, does not destroy any iterators and does not changethe distance between <tt>first</tt> and <tt>last</tt>. (There's no way that itcould do anything of the sort.) So, for example, if <tt>V</tt> is a<A href="Vector.html">vector</A>, <tt>remove(V.begin(), V.end(), 0)</tt> does not change<tt>V.size()</tt>: <tt>V</tt> will contain just as many elements as it did before.<tt>Unique</tt> returns an iterator that points to the end of the resultingrange after elements have been removed from it; it follows that theelements after that iterator are of no interest. If you are operatingon a <A href="Sequence.html">Sequence</A>, you may wish to use the <A href="Sequence.html">Sequence</A>'s <tt>erase</tt>member function to discard those elements entirely.<P><A name="2">[2]</A>Strictly speaking, the first version of <tt>unique</tt> is redundant:you can achieve the same functionality by using an object of class<tt><A href="equal_to.html">equal_to</A></tt> as the <A href="BinaryPredicate.html">Binary Predicate</A> argument. The first versionis provided strictly for the sake of convenience: testing for equalityis an important special case.<P><A name="3">[3]</A><tt>BinaryPredicate</tt> is not required to be an equivalencerelation. You should be cautious, though, about using <tt>unique</tt> with a<A href="BinaryPredicate.html">Binary Predicate</A> that is not an equivalence relation: you couldeasily get unexpected results.<h3>See also</h3><tt><A href="BinaryPredicate.html">Binary Predicate</A></tt>, <tt><A href="remove.html">remove</A></tt>, <tt><A href="remove_if.html">remove_if</A></tt>, <tt><A href="unique_copy.html">unique_copy</A></tt>,<tt><A href="adjacent_find.html">adjacent_find</A></tt>, <!-- start footer --><!-- Footer Begins --><STYLE TYPE="text/css"><!--TD.footer, TD.footer A{ font-family: Arial, helvetica, sans-serif; font-size: 8pt;}A.home {font-family: Arial, helvetica, sans-serif;}--></STYLE><P><A CLASS="home" HREF="index.html">STL Home</A><P><TABLE WIDTH="600" CELLPADDING="0" CELLPADDING="0" BORDER="0"> <TR> <TD ALIGN="RIGHT" CLASS="footer"><A HREF="/company_info/terms.html" TARGET="_top">terms of use</A> | <A HREF="/company_info/privacy.html" TARGET="_top">privacy policy</A></TD> <TD ALIGN="CENTER" CLASS="footer"> | </TD> <TD ALIGN="LEFT" CLASS="footer"><A HREF="/cgi-bin/feedback/" TARGET="_top">contact us</A></TD> </TR><TR> <TD ALIGN="RIGHT" CLASS="footer">Copyright © 1993-2003 Silicon Graphics, Inc. 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