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| <TITLE>transform()</TITLE> |
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| <H2>transform()</H2> |
| <P><B>Library:</B> <A HREF="2-9.html">Algorithms</A></P> |
| |
| <PRE><HR><B><I>Function</I></B><HR></PRE> |
| |
| <UL> |
| <LI><A HREF="#sec1">Local Index</A></LI> |
| <LI><A HREF="#sec2">Summary</A></LI> |
| <LI><A HREF="#sec3">Synopsis</A></LI> |
| <LI><A HREF="#sec4">Description</A></LI> |
| <LI><A HREF="#sec5">Complexity</A></LI> |
| <LI><A HREF="#sec6">Example</A></LI> |
| <LI><A HREF="#sec7">Standards Conformance</A></LI> |
| </UL> |
| <A NAME="sec1"><H3>Local Index</H3></A> |
| No Entries |
| <A NAME="sec2"><H3>Summary</H3></A> |
| <P>Algorithm that applies an operation to a range of values in a collection and stores the result</P> |
| <A NAME="sec3"><H3>Synopsis</H3></A> |
| |
| <PRE>#include <algorithm> |
| |
| namespace std { |
| template <class InputIterator, class OutputIterator, |
| class UnaryOperation> |
| OutputIterator |
| transform(InputIterator start, InputIterator finish, |
| OutputIterator result, UnaryOperation op); |
| |
| template <class InputIterator1, class InputIterator2, |
| class OutputIterator, class BinaryOperation> |
| OutputIterator |
| transform(InputIterator1 start1, InputIterator1 finish1, |
| InputIterator2 start2, OutputIterator result, |
| BinaryOperation binary_op); |
| } |
| </PRE> |
| <A NAME="sec4"><H3>Description</H3></A> |
| <P>The <SAMP>transform()</SAMP> algorithm has two forms. The first form applies unary operation <SAMP>op</SAMP> to each element of the range <SAMP>[start, finish)</SAMP>, and assigns the result to the element pointed to by the output iterator <SAMP>result</SAMP>. For example, this version of <SAMP>transform()</SAMP> could be used to square each element in a <B><I><A HREF="vector.html">vector</A></I></B>. If the output iterator (<SAMP>result</SAMP>) is the same as the input iterator used to traverse the range, <SAMP>transform()</SAMP> performs its transformation in place.</P> |
| <P>The second form of <SAMP>transform()</SAMP> applies a binary operation, <SAMP>binary_op</SAMP>, to corresponding elements in the range <SAMP>[start1, finish1)</SAMP> and the range that begins at <SAMP>start2</SAMP>, and assigns the result to the element pointed to by <SAMP>result</SAMP>. For example, <SAMP>transform()</SAMP> can be used to add corresponding elements in two sequences, and store the set of sums in a third. The algorithm assumes, but does not check, that the second sequence has at least as many elements as the first sequence. Note that the output iterator <SAMP>result</SAMP> can be a third sequence, or either of the two input sequences.</P> |
| <P>Formally, <SAMP>transform()</SAMP> assigns through every iterator <SAMP>i</SAMP> in the range <SAMP>[result, result + (finish1 - start1))</SAMP> a new corresponding value equal to:</P> |
| <P><SAMP>op(*(start1 + (i - result))</SAMP></P> |
| <P>or: </P> |
| <P><SAMP>binary_op(*(start1 + (i - result), *(start2 + (i - result)))</SAMP></P> |
| <P><SAMP>transform()</SAMP> returns <SAMP>result + (finish1 - start1)</SAMP>. <SAMP>op</SAMP> and <SAMP>binary_op</SAMP> must not have any side effects. <SAMP>result</SAMP> may be equal to <SAMP>start</SAMP> in case of unary transform, or to <SAMP>start1</SAMP> or <SAMP>start2</SAMP> in case of binary transform. </P> |
| <A NAME="sec5"><H3>Complexity</H3></A> |
| <P>Exactly <SAMP>finish1 - start1 </SAMP>applications of <SAMP>op</SAMP> or <SAMP>binary_op </SAMP>are performed. </P> |
| <A NAME="sec6"><H3>Example</H3></A> |
| |
| <UL><PRE>// |
| // trnsform.cpp |
| // |
| |
| #include <algorithm> // for transform |
| #include <functional> // for multiplies |
| #include <deque> // for deque |
| #include <iostream> // for cout, endl |
| #include <iomanip> // for setw |
| |
| |
| int main () |
| { |
| typedef std::deque<int, std::allocator<int> > Deque; |
| |
| // Initialize a deque with an array of integers. |
| const Deque::value_type a [] = { 99, 264, 126, 330, 132 }; |
| const Deque::value_type b [] = { 280, 105, 220, 84, 210 }; |
| |
| Deque d1 (a, a + sizeof a / sizeof *a); |
| Deque d2 (b, b + sizeof b / sizeof *b); |
| |
| // Print the original values. |
| std::cout << "The following pairs of numbers: \n "; |
| Deque::iterator i1; |
| for (i1 = d1.begin(); i1 != d1.end(); ++i1) |
| std::cout << std::setw (6) << *i1 << " "; |
| |
| std::cout << "\n "; |
| for (i1 = d2.begin(); i1 != d2.end(); ++i1) |
| std::cout << std::setw (6) << *i1 << " "; |
| |
| // transform the numbers in one sequence to |
| // their factorials and store the results in |
| // another sequence |
| std::transform (d1.begin (), d1.end (), |
| d2.begin (), d1.begin (), |
| std::multiplies<int>()); |
| |
| // Display the results. |
| std::cout << "\n\nHave the products: \n "; |
| for (i1 = d1.begin (); i1 != d1.end (); ++i1) |
| std::cout << std::setw (6) << *i1 << " "; |
| |
| std::cout << std::endl; |
| |
| return 0; |
| } |
| |
| |
| |
| Program Output: |
| </PRE></UL> |
| <UL><PRE>The following pairs of numbers: |
| 99 264 126 330 132 |
| 280 105 220 84 210 |
| |
| Have the products: |
| 27720 27720 27720 27720 27720 |
| </PRE></UL> |
| <A NAME="sec7"><H3>Standards Conformance</H3></A> |
| <P><I>ISO/IEC 14882:1998 -- International Standard for Information Systems -- Programming Language C++, Section 25.2.3</I></P> |
| |
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