## Understanding equal_range

`std::equal_range` is a general purpose standard algorithm used to find a sub-range of values in a given sorted or at least partitioned range. In this post, I will explain how the algorithm works.

Skip to content
# algorithms

## Understanding equal_range

## Transform and reduce alternatives

`std::equal_range` is a general purpose standard algorithm used to find a sub-range of values in a given sorted or at least partitioned range. In this post, I will explain how the algorithm works.

Transform-reduce is a pattern in which a set of data is first modified by applying a transformation on each of the elements and then it is reduced to a single value. In C++, this can be implemented straightforwardly with `std::transform` and `std::accumulate`. In C++17, an alternative for `std::accumulate` is available; `std::reduce` sums a range of elements just like `std::accumulate`, except that it does so out of order. That means you cannot use it with operators that are not communicative or associative (including overloads of `operator+` that don’t exhibit these properties). On the other hand, there is yet another algorithm called `std::transform_reduce` that applies a functor to all the elements of a range and then reduces them, all in an out of order manner. And then, there are also parallel versions of these algorithms. In this post, I will try to compare the performance of these possible alternatives for implementing transform-reduce.