Removing Duplicates from a Range

To remove duplicates from a range using standard algorithms, you can use a combination of std::ranges::sort() and std::ranges::unique().

This approach ensures that the range is first sorted, which is a prerequisite for std::ranges::unique() to work correctly.

Here is an example demonstrating this process:

1#include <algorithm>
2#include <iostream>
3#include <ranges>
4#include <vector>
5
6int main() {
7  std::vector<int> numbers{5, 3, 8, 3, 2, 8, 1, 5};
8
9  // Sort the range first
10  std::ranges::sort(numbers);
11
12  // Remove duplicates
13  auto last = std::ranges::unique(numbers);
14  numbers.erase(last.begin(), numbers.end());  
15
16  for (int n : numbers) {
17    std::cout << n << ", ";
18  }
19}

11, 2, 3, 5, 8,

In this example:

1. std::ranges::sort(numbers) sorts the elements in the numbers vector.
2. std::ranges::unique(numbers) rearranges the elements such that each unique element appears only once, and returns a subrange of the unique elements.
3. numbers.erase(last.begin(), numbers.end()) removes the duplicate elements from the vector.

This approach is efficient and leverages the power of the C++ standard library's range algorithms.

Alternatively, you can use a std::set to remove duplicates, which automatically handles uniqueness but does not preserve the original order:

1#include <iostream>
2#include <set>
3#include <vector>
4
5int main() {
6  std::vector<int> numbers{5, 3, 8, 3, 2, 8, 1, 5};
7
8  // Use a set to remove duplicates
9  std::set<int> unique_numbers(
10    numbers.begin(), numbers.end());
11
12  for (int n : unique_numbers) {
13    std::cout << n << ", ";
14  }
15}

11, 2, 3, 5, 8,

Using a std::set is straightforward but does not maintain the original order of elements. If preserving order is important, you should use the std::ranges::sort() and std::ranges::unique() approach.

For better performance, especially with large datasets, the sorting and unique algorithms are generally preferred as they are optimized for such operations in the standard library.