From 7cbb25c5469a1ecbb99529faaef89ce55e63671b Mon Sep 17 00:00:00 2001
From: coolneng <akasroua@gmail.com>
Date: Mon, 21 Jun 2021 17:54:37 +0200
Subject: [PATCH] Add local search module

---
 src/local_search.py | 75 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)
 create mode 100644 src/local_search.py

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