Reverse direction of instant runoff

app.py

@@ -173,7 +173,7 @@ def vote_date():
             (session["user"]["id"], meet_id,))
     dates = csr.fetchall()
 
-    result = instantrunoff_forward(meet_id, "date")
+    result = instantrunoff_backward(meet_id, "date")
     log.debug("result = %s", result)
 
     csr.execute(
@@ -194,7 +194,7 @@ def vote_date():
 
 @app.get("/result/<int:meet_id>/date")
 def result_date(meet_id):
-    result = instantrunoff_forward(meet_id, "date")
+    result = instantrunoff_backward(meet_id, "date")
     log.debug("result = %s", result)
 
     csr = get_cursor()
@@ -251,7 +251,7 @@ def vote_time():
             (session["user"]["id"], meet_id,))
     times = csr.fetchall()
 
-    result = instantrunoff_forward(meet_id, "time")
+    result = instantrunoff_backward(meet_id, "time")
     log.debug("result = %s", result)
 
     csr.execute(
@@ -272,7 +272,7 @@ def vote_time():
 
 @app.get("/result/<int:meet_id>/time")
 def result_time(meet_id):
-    result = instantrunoff_forward(meet_id, "time")
+    result = instantrunoff_backward(meet_id, "time")
     log.debug("result = %s", result)
 
     csr = get_cursor()
@@ -327,7 +327,7 @@ def vote_place():
             (session["user"]["id"], meet_id,))
     places = csr.fetchall()
 
-    result = instantrunoff_forward(meet_id, "place")
+    result = instantrunoff_backward(meet_id, "place")
     log.debug("result = %s", result)
 
     csr.execute(
@@ -349,7 +349,7 @@ def vote_place():
 
 @app.get("/result/<int:meet_id>/place")
 def result_place(meet_id):
-    result = instantrunoff_forward(meet_id, "place")
+    result = instantrunoff_backward(meet_id, "place")
     log.debug("result = %s", result)
 
     csr = get_cursor()
@@ -373,7 +373,7 @@ def result_place(meet_id):
 @app.get("/result/<int:meet_id>/date/ballot")
 def result_ballots_date(meet_id):
     ballots = get_ballots(meet_id, "date")
-    result = instantrunoff_forward(meet_id, "date")
+    result = instantrunoff_backward(meet_id, "date")
 
     return render_template(
                 "date_result_ballots.html",
@@ -382,7 +382,7 @@ def result_ballots_date(meet_id):
 @app.get("/result/<int:meet_id>/time/ballot")
 def result_ballots_time(meet_id):
     ballots = get_ballots(meet_id, "time")
-    result = instantrunoff_forward(meet_id, "time")
+    result = instantrunoff_backward(meet_id, "time")
 
     return render_template(
                 "time_result_ballots.html",
@@ -391,7 +391,7 @@ def result_ballots_time(meet_id):
 @app.get("/result/<int:meet_id>/place/ballot")
 def result_ballots_place(meet_id):
     ballots = get_ballots(meet_id, "place")
-    result = instantrunoff_forward(meet_id, "place")
+    result = instantrunoff_backward(meet_id, "place")
 
     return render_template(
                 "place_result_ballots.html",
@@ -453,6 +453,9 @@ def runoff(ballots):
             log.debug("pos = %s", pos)
             count[r.id][pos] += 1
             log.debug("count[%d][%d]) = %d", r.id, pos, count[r.id][pos])
+    if direction == "backward":
+        result = sorted(count.keys(), key=lambda i: list(reversed(count[i])), reverse=True)
+    else:
         result = sorted(count.keys(), key=lambda i: count[i])
     log.debug("result of this round:")
     for r in result:
@@ -472,7 +475,21 @@ def instantrunoff_forward(meet_id, kind):
     result = []
     while max(len(b) for b in ballots):
         dump_ballots(ballots)
-        loser, ballots = runoff(ballots)
+        loser, ballots = runoff(ballots, "forward")
+        result.append(loser)
+    result = list(reversed(result))
+    log.debug("final result")
+    for r in result:
+        log.debug(r)
+    return result
+
+def instantrunoff_backward(meet_id, kind):
+    ballots = get_ballots(meet_id, kind)
+
+    result = []
+    while max(len(b) for b in ballots):
+        dump_ballots(ballots)
+        loser, ballots = runoff(ballots, "backward")
         result.append(loser)
     result = list(reversed(result))
     log.debug("final result")

utils/instantrunoff

@@ -7,6 +7,7 @@ import psycopg.rows
 
 def get_args():
     ap = argparse.ArgumentParser()
+    ap.add_argument("--reverse", action="store_true")
     ap.add_argument("meet", type=int)
     ap.add_argument("kind")
 
@@ -53,6 +54,9 @@ def runoff(ballots):
     for ballot in ballots:
         for pos, r in enumerate(ballot):
             count[r.id][pos] += 1
+    if args.reverse:
+        result = sorted(count.keys(), key=lambda i: list(reversed(count[i])), reverse=True)
+    else:
         result = sorted(count.keys(), key=lambda i: count[i])
     print("result of this round:")
     for r in result: