Replacement Algorithms

Replace without modifying original

How do I handle cases where std::ranges::replace() should not modify the original container but create a modified copy instead?

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To replace elements in a container without modifying the original, use std::ranges::replace_copy().

This function creates a new container with the modified elements, leaving the original unchanged. Here's an example:

#include <algorithm>
#include <iostream>
#include <vector>

int main() {
  std::vector<int> Source{1, 2, 3, 3, 3, 4, 5};
  std::vector<int> Destination(Source.size());

  std::ranges::replace_copy(
    Source, Destination.begin(), 3, 0);

  std::cout << "Original: ";
  for (const auto &num : Source) {
    std::cout << num << ", ";
  }
  std::cout << "\nModified: ";
  for (const auto &num : Destination) {
    std::cout << num << ", ";
  }
}
Original: 1, 2, 3, 3, 3, 4, 5, 
Modified: 1, 2, 0, 0, 0, 4, 5,

In this example, std::ranges::replace_copy() copies elements from Source to Destination. It replaces elements equal to 3 with 0 in the Destination container, but Source remains unchanged.

This approach is useful when you need to preserve the original data for further use or comparison. By creating a new container, you can apply transformations without risking unwanted side effects on the original dataset.

Always ensure that the destination container has sufficient size to accommodate the copied elements. You can resize the destination container beforehand, as shown in the example.

Answers to questions are automatically generated and may not have been reviewed.

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