View that skips similar adjacent items

Range-v3 has views::unique. However, the standard library currently does not have a similar one, although it is marked as Tier 2 on P2760.

However, you can assemble something similar using existing adaptors:

/ const / auto ret = v | std::views::chunkby(std::ranges::equalto{})
                         | std::views::transform(std::views::take(1))
                         | std::views::join;

Demo

Note that const-qualified cannot be used because chunkbyview is not const-iterable.

#include 
#include 
#include 
#include 
int main() {
  std::vector v{1, 2, 1, 1, 3, 3, 3, 4, 5, 4};
  fmt::println("{}", v);
  // [1, 2, 1, 1, 3, 3, 3, 4, 5, 4]
  const std::span ret(v.begin(), std::ranges::unique(v).begin());
  fmt::println("{}", ret);
  // [1, 2, 1, 3, 4, 5, 4]
}