genetic_algorithms 2.2.0

Library for solving genetic algorithm problems
Documentation 
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//! Age-based survivor selection.
//!
//! Retains the youngest individuals (lowest age) after parents and offspring
//! have been merged. This strategy favours fresh genetic material and
//! prevents long-lived individuals from dominating the population.

pub(crate) use crate::traits::ChromosomeT;
use log::{debug, trace};

/// Age-based survivor selection: sorts individuals by age (youngest first)
/// and keeps the top `population_size`.
///
/// # Arguments
///
/// * `chromosomes` - Combined parents + offspring (modified in place).
/// * `population_size` - Desired population size after selection.
pub fn age_based<U: ChromosomeT>(chromosomes: &mut Vec<U>, population_size: usize) {
    //We first sort the chromosomes by their fitness
    debug!(target="survivor_events", method="age_based"; "Starting age based survivor method");
    chromosomes.sort_by_key(|a| std::cmp::Reverse(a.age()));

    // Drop surplus individuals from the tail in O(1) instead of
    // loop of Vec::remove (O(N) per removal).
    trace!(target="survivor_events", method="age_based"; "Chromosomes length {} - population size {}", chromosomes.len(), population_size);
    if chromosomes.len() > population_size {
        chromosomes.truncate(population_size);
    }
    debug!(target="survivor_events", method="age_based"; "Age based survivor method finished");
}