diff --git a/src/local_search.py b/src/local_search.py new file mode 100644 index 0000000..06f6834 --- /dev/null +++ b/src/local_search.py @@ -0,0 +1,75 @@ +from numpy.random import choice, seed, randint +from pandas import DataFrame + + +def get_row_distance(source, destination, data): + row = data.query( + """(source == @source and destination == @destination) or \ + (source == @destination and destination == @source)""" + ) + return row["distance"].values[0] + + +def compute_distance(element, solution, data): + accumulator = 0 + distinct_elements = solution.query(f"point != {element}") + for _, item in distinct_elements.iterrows(): + accumulator += get_row_distance( + source=element, + destination=item.point, + data=data, + ) + return accumulator + + +def get_first_random_solution(n, m, data): + solution = DataFrame(columns=["point", "distance"]) + seed(42) + solution["point"] = choice(n, size=m, replace=False) + solution["distance"] = solution["point"].apply( + func=compute_distance, solution=solution, data=data + ) + return solution + + +def element_in_dataframe(solution, element): + duplicates = solution.query(f"point == {element}") + return not duplicates.empty + + +def replace_worst_element(previous, n, data): + solution = previous.copy() + worst_index = solution["distance"].astype(float).idxmin() + random_element = randint(n) + while element_in_dataframe(solution=solution, element=random_element): + random_element = randint(n) + solution["point"].loc[worst_index] = random_element + solution["distance"].loc[worst_index] = compute_distance( + element=solution["point"].loc[worst_index], solution=solution, data=data + ) + return solution + + +def get_random_solution(previous, n, data): + solution = replace_worst_element(previous, n, data) + while solution["distance"].sum() <= previous["distance"].sum(): + solution = replace_worst_element(previous=solution, n=n, data=data) + return solution + + +def explore_neighbourhood(element, n, data, max_iterations=100000): + neighbourhood = [] + neighbourhood.append(element) + for _ in range(max_iterations): + previous_solution = neighbourhood[-1] + neighbour = get_random_solution(previous=previous_solution, n=n, data=data) + neighbourhood.append(neighbour) + return neighbour + + +def local_search(n, m, data): + first_solution = get_first_random_solution(n, m, data) + best_solution = explore_neighbourhood( + element=first_solution, n=n, data=data, max_iterations=100 + ) + return best_solution