Category: algorithms
Component type: function
Prototype Transform is an overloaded name; there are actually two transform functions.
template <class InputIterator, class OutputIterator, class UnaryFunction>
OutputIterator transform(InputIterator first, InputIterator last, OutputIterator result, UnaryFunction op);
template <class InputIterator1, class InputIterator2, class OutputIterator, class BinaryFunction>
OutputIterator transform (InputIterator1 first1, InputIterator1 last1, InputIterator2 first2, OutputIterator result, BinaryFunction binary_op);
Description Transform performs an operation on objects; there are two versions of transform, one of which uses a single range of Input Iterators and one of which uses two ranges of Input Iterators.
The first version of transform performs the operation op(*i) for each iterator i in the range [first, last) , and assigns the result of that operation to *o, where o is the corresponding output iterator. That is, for each n such that 0 <= n < last – first, it performs the assignment *(result + n) = op(*(first + n)). The return value is result + (last – first).
The second version of transform is very similar, except that it uses a Binary Function instead of a Unary Function: it performs the operation op(*i1, *i2) for each iterator i1 in the range [first1, last1) and assigns the result to *o, where i2 is the corresponding iterator in the second input range and where o is the corresponding output iterator. That is, for each n such that 0 <= n < last1 – first1, it performs the assignment *(result + n) = op(*(first1 + n), *(first2 + n). The return value is result + (last1 – first1).
Note that transform may be used to modify a sequence 'in place': it is permissible for the iterators first and result to be the same. [1]
Definition Defined in the standard header algorithm, and in the nonstandard backward-compatibility header algo.h.
Requirements on types For the first (unary) version:
• InputIterator must be a model of Input Iterator.
• OutputIterator must be a model of Output Iterator.
• UnaryFunction must be a model of Unary Function.
• InputIterator's value type must be convertible to UnaryFunction's argument type.
• UnaryFunction's result type must be convertible to a type in OutputIterator's set of value types.
For the second (binary) version:
• InputIterator1 and InputIterator2 must be models of Input Iterator.
• OutputIterator must be a model of Output Iterator.
• BinaryFunction must be a model of Binary Function.
• InputIterator1's and InputIterator2's value types must be convertible, respectively, to BinaryFunction's first and second argument types.
• UnaryFunction's result type must be convertible to a type in OutputIterator's set of value types.
Preconditions For the first (unary) version:
• [first, last) is a valid range.
• result is not an iterator within the range [first+1, last) . [1]
• There is enough space to hold all of the elements being copied. More formally, the requirement is that [result, result + (last – first)) is a valid range.
For the second (binary) version:
• [first1, last1) is a valid range.
• [first2, first2 + (last1 – first1)) is a valid range.
• result is not an iterator within the range [first1+1, last1) or [first2 + 1, first2 + (last1 – first1)).
• There is enough space to hold all of the elements being copied. More formally, the requirement is that [result, result + (last1 – first1)) is a valid range.
Complexity Linear. The operation is applied exactly last – first times in the case of the unary version, or last1 – first1 in the case of the binary version.
Example Replace every number in an array with its negative.
const int N = 1000;
double A[N];
iota (A, A+N, 1);
transform(A, A+N, A, negate<double>());
