Finish social-preference and social-choice functions for borda method.

deliberate/borda.scm

@@ -1,6 +1,6 @@
 (define-module (deliberate borda)
   #:use-module (deliberate utils)
-  #:export (borda-score))
+  #:export (borda-score social-choice-borda social-preference-borda))
 
 (define (borda-score alternatives ranked)
   ;; Check whether all alternatives have been scored
@@ -18,3 +18,30 @@
 	    (cons (cons alt (length remaining))
 		  (borda-score remaining (cdr ranked))))
 	  )))
+
+(define (profile->scores alternatives profile)
+  (apply append
+	 (map (lambda (pair)
+		(borda-score alternatives (cdr pair)))
+	      profile)))
+
+(define (groups->totals groups)
+  (map (lambda (elt)
+	 (cons (car elt)
+	       (reduce + 0 (map cdr (cdr elt)))))
+       groups))
+
+(define (profile-borda-totals alternatives profile)
+  (let* ((scores (profile->scores alternatives profile))
+	 (groups (group-by car scores))
+	 (totals (groups->totals groups)))
+    totals))
+
+;; TODO - handle ties
+(define (social-preference-borda alternatives profile)
+  (let ((totals (profile-borda-totals alternatives profile)))
+    ;; We use > instead of < for to rank in decreasing score order
+    (map (compose list car) (sort totals (lambda (x y) (> (cdr x) (cdr y)))))))
+
+(define (social-choice-borda alternatives profile)
+  (car (social-preference-borda alternatives profile)))

test-borda.scm

@@ -13,12 +13,6 @@
 
 (borda-score test-alts test-pref)
 
-(define (profile-borda-scores alternatives profile)
-  (apply append
-	 (map (lambda (pair)
-		(borda-score alternatives (cdr pair)))
-	      profile)))
+(social-preference-borda test-alts test-profile)
 
-(define test-scores (profile-borda-scores test-alts test-profile))
-
-(define test-score-groups (group-by car test-scores))
+(social-choice-borda test-alts test-profile)