Shuffling a Partial Range

Yes, you can use std::ranges::shuffle() with a partial range of a container. This is useful when you want to randomize only a specific portion of a container while leaving the rest intact.

Using std::ranges::shuffle() with a Partial Range

To shuffle a partial range, you can provide iterators that define the subrange you want to shuffle. Here's an example:

1#include <algorithm>
2#include <iostream>
3#include <random>
4#include <vector>
5
6int main() {
7  std::vector<int> data{1, 2, 3, 4, 5, 6, 7, 8};
8
9  std::random_device rd;
10  std::mt19937 gen(rd());
11
12  // Shuffle only the first 5 elements
13  std::ranges::shuffle(data.begin(),
14    data.begin() + 5, gen);
15
16  for (const auto& value : data) {
17    std::cout << value << " ";
18  }
19}

14 1 3 5 2 6 7 8

Step-by-Step Guide

1. Define the Range: Identify the portion of the container you want to shuffle. Use iterators to specify the start and end of this subrange.
2. Provide a Random Number Generator (RNG): std::ranges::shuffle() requires an RNG. Here, we use std::mt19937 from the <random> header.
3. Call the std::ranges::shuffle algorithm: Pass the iterators for the subrange and the RNG to std::ranges::shuffle().

Practical Example

Consider a scenario where you want to shuffle only the middle part of a vector:

1#include <algorithm>
2#include <iostream>
3#include <random>
4#include <vector>
5
6int main() {
7  std::vector<int> numbers{
8    10, 20, 30, 40, 50, 60, 70, 80, 90, 100};
9
10  std::random_device rd;
11  std::mt19937 gen(rd());
12
13  // Shuffle elements from index 3 to 7
14  std::ranges::shuffle(
15    numbers.begin() + 3,
16    numbers.begin() + 8,
17    gen
18  );
19
20  for (const auto& num : numbers) {
21    std::cout << num << " ";
22  }
23}

110 20 30 80 70 60 40 50 90 100

Considerations

• Range Boundaries: Ensure that the iterators provided do not exceed the container's boundaries to avoid undefined behavior.
• Random Device: Using std::random_device for seeding the RNG ensures better randomness compared to a fixed seed.

Conclusion

Using std::ranges::shuffle() with a partial range of a container is straightforward.

By specifying the appropriate iterators, you can shuffle any subrange within your container, giving you flexibility in how you randomize elements.

This approach is particularly useful in scenarios where only a segment of data needs to be randomized.