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<Head>
<Title>transform</Title>
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<H1>transform</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>
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<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>Transform</tt> is an overloaded name; there are actually two <tt>transform</tt>
functions.
<pre>
template <class <A href="InputIterator.html">InputIterator</A>, class <A href="OutputIterator.html">OutputIterator</A>, class <A href="UnaryFunction.html">UnaryFunction</A>>
OutputIterator transform(InputIterator first, InputIterator last,
OutputIterator result, UnaryFunction op);
template <class <A href="InputIterator.html">InputIterator</A>1, class <A href="InputIterator.html">InputIterator</A>2, class <A href="OutputIterator.html">OutputIterator</A>,
class <A href="BinaryFunction.html">BinaryFunction</A>>
OutputIterator transform(InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, OutputIterator result,
BinaryFunction binary_op);
</pre>
<h3>Description</h3>
<tt>Transform</tt> performs an operation on objects; there are two versions
of <tt>transform</tt>, one of which uses a single range of <A href="InputIterator.html">Input Iterators</A>
and one of which uses two ranges of <A href="InputIterator.html">Input Iterators</A>.
<P>
The first version of <tt>transform</tt> performs the operation <tt>op(*i)</tt>
for each iterator <tt>i</tt> in the range <tt>[first, last)</tt>, and assigns
the result of that operation to <tt>*o</tt>, where <tt>o</tt> is the corresponding
output iterator. That is, for each <tt>n</tt> such that <tt>0 <= n < last - first</tt>,
it performs the assignment <tt>*(result + n) = op(*(first + n))</tt>.
The return value is <tt>result + (last - first)</tt>.
<P>
The second version of <tt>transform</tt> is very similar, except that it
uses a <A href="BinaryFunction.html">Binary Function</A> instead of a <A href="UnaryFunction.html">Unary Function</A>:
it performs the operation <tt>op(*i1, *i2)</tt> for each iterator <tt>i1</tt> in the
range <tt>[first1, last1)</tt> and assigns the result to <tt>*o</tt>, where
<tt>i2</tt> is the corresponding iterator in the second input range and
where <tt>o</tt> is the corresponding output iterator. That is,
for each <tt>n</tt> such that <tt>0 <= n < last1 - first1</tt>,
it performs the assignment <tt>*(result + n) = op(*(first1 + n), *(first2
+ n)</tt>. The return value is <tt>result + (last1 - first1)</tt>.
<P>
Note that <tt>transform</tt> may be used to modify a sequence "in place":
it is permissible for the iterators <tt>first</tt> and <tt>result</tt> to be the same. <A href="#1">[1]</A>
<h3>Definition</h3>
Defined in the standard header <A href="algorithm">algorithm</A>, and in the nonstandard
backward-compatibility header <A href="algo.h">algo.h</A>.
<h3>Requirements on types</h3>
For the first (unary) version:
<UL>
<LI>
<tt>InputIterator</tt> must be a model of <A href="InputIterator.html">Input Iterator</A>.
<LI>
<tt>OutputIterator</tt> must be a model of <A href="OutputIterator.html">Output Iterator</A>.
<LI>
<tt>UnaryFunction</tt> must be a model of <A href="UnaryFunction.html">Unary Function</A>.
<LI>
<tt>InputIterator</tt>'s value type must be
convertible to <tt>UnaryFunction</tt>'s argument type.
<LI>
<tt>UnaryFunction</tt>'s result type must be convertible to a type in
<tt>OutputIterator</tt>'s set of value types.
</UL>
For the second (binary) version:
<UL>
<LI>
<tt>InputIterator1</tt> and <tt>InputIterator2</tt>
must be models of <A href="InputIterator.html">Input Iterator</A>.
<LI>
<tt>OutputIterator</tt> must be a model of <A href="OutputIterator.html">Output Iterator</A>.
<LI>
<tt>BinaryFunction</tt> must be a model of <A href="BinaryFunction.html">Binary Function</A>.
<LI>
<tt>InputIterator1</tt>'s and <tt>InputIterator2</tt>'s value types must
be convertible, respectively, to <tt>BinaryFunction</tt>'s first and second
argument types.
<LI>
<tt>UnaryFunction</tt>'s result type must be convertible
to a type in <tt>OutputIterator</tt>'s set of value types.
</UL>
<h3>Preconditions</h3>
For the first (unary) version:
<UL>
<LI>
<tt>[first, last)</tt> is a valid range.
<LI>
<tt>result</tt> is not an iterator within the range <tt>[first+1, last)</tt>. <A href="#1">[1]</A>
<LI>
There is enough space to hold all of the elements being copied.
More formally, the requirement is that
<tt>[result, result + (last - first))</tt> is a valid range.
</UL>
For the second (binary) version:
<UL>
<LI>
<tt>[first1, last1)</tt> is a valid range.
<LI>
<tt>[first2, first2 + (last1 - first1))</tt> is a valid range.
<LI>
<tt>result</tt> is not an iterator within the range <tt>[first1+1, last1)</tt>
or <tt>[first2 + 1, first2 + (last1 - first1))</tt>.
<LI>
There is enough space to hold all of the elements being copied.
More formally, the requirement is that
<tt>[result, result + (last1 - first1))</tt> is a valid range.
</UL>
<h3>Complexity</h3>
Linear. The operation is applied exactly <tt>last - first</tt> times
in the case of the unary version, or <tt>last1 - first1</tt> in the case
of the binary version.
<h3>Example</h3>
Replace every number in an array with its negative.
<pre>
const int N = 1000;
double A[N];
<A href="iota.html">iota</A>(A, A+N, 1);
transform(A, A+N, A, <A href="negate.html">negate</A><double>());
</pre>
<P>
Calculate the sum of two vectors, storing the result in a third vector.
<pre>
const int N = 1000;
<A href="Vector.html">vector</A><int> V1(N);
<A href="Vector.html">vector</A><int> V2(N);
<A href="Vector.html">vector</A><int> V3(N);
<A href="iota.html">iota</A>(V1.begin(), V1.end(), 1);
<A href="fill.html">fill</A>(V2.begin(), V2.end(), 75);
assert(V2.size() >= V1.size() && V3.size() >= V1.size());
transform(V1.begin(), V1.end(), V2.begin(), V3.begin(),
<A href="plus.html">plus</A><int>());
</pre>
<h3>Notes</h3>
<P><A name="1">[1]</A>
The <A href="OutputIterator.html">Output Iterator</A> <tt>result</tt> is not permitted to be the same as
any of the <A href="InputIterator.html">Input Iterators</A> in the range <tt>[first, last)</tt>, with the
exception of <tt>first</tt> itself. That is:
<tt>transform(V.begin(), V.end(), V.begin(), fabs)</tt> is valid, but
<tt>transform(V.begin(), V.end(), V.begin() + 1, fabs)</tt> is not.
<h3>See also</h3>
The <A href="functors.html">function object overview</A>, <tt><A href="copy.html">copy</A></tt>, <tt><A href="generate.html">generate</A></tt>,
<tt><A href="fill.html">fill</A></tt>
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