filter_events.cpp

#include <fmt/format.h>
#include <range/v3/view.hpp>
#include <vector>

struct event {
  int created = 0;
  int status = 0;
};

std::vector<event> create_events() {
  std::vector<event> v;

  v.push_back({ 101, 1 });
  v.push_back({ 102, 2 });
  v.push_back({ 103, 1 });
  v.push_back({ 104, 2 });

  v.push_back({ 201, 2 });
  v.push_back({ 202, 1 });
  v.push_back({ 203, 1 });
  v.push_back({ 204, 2 });
  v.push_back({ 205, 2 });
  v.push_back({ 206, 1 });
  v.push_back({ 207, 1 });

  return v;
}

int main() {
  const auto events = create_events();

  constexpr auto group_events = ranges::views::group_by([](const auto& lhs, const auto& rhs) {
    return lhs.created / 100 == rhs.created / 100;
  });

  constexpr auto drop_1 = ranges::views::drop_while([](const auto& event) {
    return event.status == 1;
  });

  constexpr auto drop_2 = ranges::views::drop_while([](const auto& event) {
    return event.status == 2;
  });

  constexpr auto filter_order = ranges::views::adjacent_filter([](const event& lhs, const event& rhs) {
    return lhs.status != rhs.status;
  });

  constexpr auto reverse = ranges::views::reverse;

  constexpr auto filter_group = drop_2 | reverse | drop_1 | reverse | filter_order;

  for (const auto& group : events | group_events) {
    fmt::print("group: {}\n", group.front().created / 100);
    for (const auto& event : group | filter_group) {
      fmt::print("{} -> {}\n", event.created, event.status);
    }
    fmt::print("\n");
  }
}

Output:

group: 1
101 -> 1
102 -> 2
103 -> 1
104 -> 2

group: 2
202 -> 1
204 -> 2