Category: algorithms | Component type: function |
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);
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]
const int N = 1000; double A[N]; iota(A, A+N, 1); transform(A, A+N, A, negate<double>());
Calculate the sum of two vectors, storing the result in a third vector.
const int N = 1000; vector<int> V1(N); vector<int> V2(N); vector<int> V3(N); iota(V1.begin(), V1.end(), 1); fill(V2.begin(), V2.end(), 75); assert(V2.size() >= V1.size() && V3.size() >= V1.size()); transform(V1.begin(), V1.end(), V2.begin(), V3.begin(), plus<int>());
[1] The Output Iterator result is not permitted to be the same as any of the Input Iterators in the range [first, last), with the exception of first itself. That is: transform(V.begin(), V.end(), V.begin(), fabs) is valid, but transform(V.begin(), V.end(), V.begin() + 1, fabs) is not.
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