From c40f1f70f445b162e987fe4e0395bcef9d23be25 Mon Sep 17 00:00:00 2001
From: Ryan Boldi <ryan.boldi123@gmail.com>
Date: Thu, 5 Jan 2023 12:40:15 +0100
Subject: [PATCH] added fitness proportionate selection + tests

---
 src/propeller/selection.cljc       | 20 +++++++++++++++++++-
 test/propeller/selection_test.cljc | 23 +++++++++++++++++++++++
 2 files changed, 42 insertions(+), 1 deletion(-)
 create mode 100644 test/propeller/selection_test.cljc

diff --git a/src/propeller/selection.cljc b/src/propeller/selection.cljc
index 487ecf2..b89ab51 100755
--- a/src/propeller/selection.cljc
+++ b/src/propeller/selection.cljc
@@ -21,9 +21,27 @@
                        survivors)
                (rest cases))))))
 
+(defn fitness-proportionate-selection 
+  "Selects an individual from the population using a fitness proportionate selection."
+  [pop argmap]
+  (let [pop-fits (->> pop ;convert from error to fitness, where fitness (probability) is (1/ (1+ tot_err))
+                      (map #(assoc % :fitness (/ 1 (inc (:total-error %))))))
+        pop-total-fit (->> pop-fits
+                           (map :fitness)
+                           (reduce +))
+        random-num (* (rand) pop-total-fit) 
+        sorted-by-fitness (->> pop-fits
+                               (sort-by :fitness)
+                               (reverse))]
+    (loop [tot (:fitness (first sorted-by-fitness)) individuals sorted-by-fitness]
+      (if (< random-num tot)
+        (first individuals)
+        (recur (+ tot (:fitness (first (rest individuals)))) (rest individuals))))))
+
 (defn select-parent
   "Selects a parent from the population using the specified method."
   [pop argmap]
   (case (:parent-selection argmap)
     :tournament (tournament-selection pop argmap)
-    :lexicase (lexicase-selection pop argmap)))
+    :lexicase (lexicase-selection pop argmap)
+    :roulette (fitness-proportionate-selection pop argmap)))
\ No newline at end of file
diff --git a/test/propeller/selection_test.cljc b/test/propeller/selection_test.cljc
new file mode 100644
index 0000000..669d873
--- /dev/null
+++ b/test/propeller/selection_test.cljc
@@ -0,0 +1,23 @@
+(ns propeller.selection-test
+  (:require [clojure.test :as t]
+            [propeller.selection :as s]))
+
+
+(t/deftest roulette-selection-test
+  (t/testing "fitness proportionate selection"
+    (t/testing "should correctly define the probabilities of selection"
+      (t/is (let [ret (s/fitness-proportionate-selection '({:index 0 :total-error 0}
+                                                           {:index 1 :total-error 1}
+                                                           {:index 2 :total-error 1}
+                                                           {:index 3 :total-error 1}) {:empty :argmap})]
+              (case (:index ret)
+                0 (= (:fitness ret) 1) ;if we selected index 0, check that fitness is correctly calculated to 1
+                (= (:fitness ret) 1/2)
+                ))))
+    (t/testing "should always return the same individual if there is only one"
+      (t/testing "desipte it having bad error"
+        (t/is (= (:index (s/fitness-proportionate-selection '({:index 99 :total-error 109012390123}) {:empty :argmap}))
+                 99)))
+      (t/testing "when it has low error"
+        (t/is (= (:index (s/fitness-proportionate-selection '({:index 22 :total-error 0}) {:empty :argmap}))
+                 22))))))
\ No newline at end of file