Counting Algorithms

Customizing Predicates for std::ranges::count_if()

How can I customize the behavior of std::ranges::count_if() for specific data types?

Abstract art representing computer programming

Customizing the behavior of std::ranges::count_if() for specific data types involves writing specialized predicate functions.

These predicates can leverage the properties and methods of the data types to determine the count criteria.

Example with Custom Class

Let's consider a custom class Player and use std::ranges::count_if() to count players with specific attributes.

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

class Player {/*...*/}; int main() { std::vector<Player> players { {"Roderick", 100, 10}, {"Anna", 50, 5}, {"Robert", 150, 12} }; int threshold = 8; auto highLevelPredicate = [&](const Player& p) { return p.isHighLevel(threshold); }; int highLevelCount = std::ranges::count_if( players, highLevelPredicate); std::cout << "Number of high-level players: " << highLevelCount; }
Number of high-level players: 2

Custom Predicate Function

In this example:

  • The Player class has an isHighLevel() method to check if a player's level exceeds a given threshold.
  • In main(), we create a lambda highLevelPredicate that binds the threshold and uses isHighLevel().
  • We pass this lambda to std::ranges::count_if() to count players above the threshold level.

General Tips

  • Use Lambdas: Lambdas are great for creating custom predicates on-the-fly.
  • Member Functions: Leverage member functions within your predicates for readability and encapsulation.
  • Capture Lists: Use lambda capture lists to bind external variables to your predicates.

By writing custom predicates, you can tailor std::ranges::count_if() to fit various complex criteria, making your code more expressive and powerful.

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

A computer programmer
Part of the course:

Professional C++

Comprehensive course covering advanced concepts, and how to use them on large-scale projects.

Free, unlimited access

This course includes:

  • 124 Lessons
  • 550+ Code Samples
  • 96% Positive Reviews
  • Regularly Updated
  • Help and FAQ
Free, Unlimited Access

Professional C++

Comprehensive course covering advanced concepts, and how to use them on large-scale projects.

Screenshot from Warhammer: Total War
Screenshot from Tomb Raider
Screenshot from Jedi: Fallen Order
Contact|Privacy Policy|Terms of Use
Copyright © 2024 - All Rights Reserved