c++stl-algorithmstd-ranges

Standard algorithm to operate on adjacent elements


std::adjacent_find looks for the first two consecutive elements that satisfies the given predicate. I am looking for other algorithms that also has a predicate that takes the (previous, current) pair. This is useful for rendering polygons, computing numerical quadrature based on sample data etc.

In addition to std::adjacent_find there is std::adjacent_difference, which can be used to implement a one-dimensional filter, but is not useful if you only want the sum of op(previous, current).

Can such functions be emulated with some kind of view from std::ranges?


Solution

  • There's no special function for this, because you can just call the binary transform std::transform(c.begin(), std::prev(c.end()), std::next(c.begin()), op). This works on the overlapping ranges [c.begin(), c.end()-1] and [c.begin()+1, c.end()].

    Similarly, other operations that take two input ranges can work on two overlapping ranges as long as they don't modify the inputs.

    This can also work with greater differences than +/-1. It should be noted that this does not work on input iterators - they're one-pass.