SpECTRE Documentation Coverage Report
Current view: top level - Utilities - CartesianProduct.hpp Hit Total Coverage
Commit: 817e13c5144619b701c7cd870655d8dbf94ab8ce Lines: 3 4 75.0 %
Date: 2024-07-19 22:17:05
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          Line data    Source code
       1           0 : // Distributed under the MIT License.
       2             : // See LICENSE.txt for details.
       3             : 
       4             : #pragma once
       5             : 
       6             : #include <array>
       7             : #include <iterator>
       8             : #include <tuple>
       9             : #include <utility>
      10             : #include <vector>
      11             : 
      12             : // This implementation is from:
      13             : // https://stackoverflow.com/questions/16686942/how-to-iterate-over-two-stl-like-containers-cartesian-product
      14             : 
      15             : namespace detail {
      16             : 
      17             : // the lambda is fully bound with one element from each of the ranges
      18             : template <class Op>
      19             : void insert_tuples(Op op) {
      20             :   // evaluating the lambda will insert the currently bound tuple
      21             :   op();
      22             : }
      23             : 
      24             : // "peel off" the first range from the remaining tuple of ranges
      25             : template <class Op, class InputIterator1, class... InputIterator2>
      26             : void insert_tuples(Op op, std::pair<InputIterator1, InputIterator1> head,
      27             :                    std::pair<InputIterator2, InputIterator2>... tail) {
      28             :   // "peel off" the elements from the first of the remaining ranges
      29             :   // NOTE: the recursion will effectively generate the multiple nested for-loops
      30             :   for (auto it = head.first; it != head.second; ++it) {
      31             :     // bind the first free variable in the lambda, and
      32             :     // keep one free variable for each of the remaining ranges
      33             :     detail::insert_tuples(
      34             :         [&op, &it](InputIterator2... elems) { op(it, elems...); }, tail...);
      35             :   }
      36             : }
      37             : 
      38             : }  // namespace detail
      39             : 
      40             : /*!
      41             :  * \ingroup UtilitiesGroup
      42             :  * \brief Fill the `result` iterator with the Cartesian product of a sequence of
      43             :  * iterators
      44             :  *
      45             :  * The `result` will hold all possible combinations of the input iterators.
      46             :  * The last dimension varies fastest.
      47             :  */
      48             : template <class OutputIterator, class... InputIterator>
      49           1 : void cartesian_product(OutputIterator result,
      50             :                        std::pair<InputIterator, InputIterator>... dimensions) {
      51             :   detail::insert_tuples(
      52             :       [&result](InputIterator... elems) {
      53             :         *result++ = std::make_tuple(*elems...);
      54             :       },
      55             :       dimensions...);
      56             : }
      57             : 
      58             : /*!
      59             :  * \ingroup UtilitiesGroup
      60             :  * \brief The Cartesian product of a sequence of arrays
      61             :  *
      62             :  * Returns a `std::array` with all possible combinations of the input arrays.
      63             :  * The last dimension varies fastest.
      64             :  *
      65             :  * \example
      66             :  * Here's an example using this function to replace a nested for loop:
      67             :  * \snippet Test_Wedge3D.cpp cartesian_product_loop
      68             :  */
      69             : template <typename... Ts, size_t... Lens>
      70           1 : std::array<std::tuple<Ts...>, (... * Lens)> cartesian_product(
      71             :     const std::array<Ts, Lens>&... dimensions) {
      72             :   std::array<std::tuple<Ts...>, (... * Lens)> result{};
      73             :   cartesian_product(result.begin(),
      74             :                     std::make_pair(dimensions.begin(), dimensions.end())...);
      75             :   return result;
      76             : }
      77             : 
      78             : /*!
      79             :  * \ingroup UtilitiesGroup
      80             :  * \brief The Cartesian product of several containers
      81             :  *
      82             :  * Returns a `std::vector` with all possible combinations of the values of the
      83             :  * input containers. The value of the last container varies fastest.
      84             :  */
      85             : template <typename... Containers>
      86           1 : std::vector<std::tuple<typename Containers::value_type...>> cartesian_product(
      87             :     const Containers&... containers) {
      88             :   std::vector<std::tuple<typename Containers::value_type...>> result{};
      89             :   cartesian_product(
      90             :       std::back_inserter(result),
      91             :       std::make_pair(std::begin(containers), std::end(containers))...);
      92             :   return result;
      93             : }

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