twfarland · March 27, 2012 11:07 · Mar 27, 2012 · Mar 27, 2012 · Mar 27, 2012
diff --git a/reddit-ranking.rkt b/reddit-ranking.rkt
@@ -1,6 +1,6 @@
 #lang racket
-(require "lite.rkt") 
-; https://raw.github.com/gist/2214946/7d16522c4feebae1745b7608801a5e5d4294b0c1/lite.rkt
+(require "connive.rkt") 
+; https://github.com/twfarland/connive
 
 ; Reddit ranking algorithms
 

diff --git a/reddit-ranking.rkt b/reddit-ranking.rkt
@@ -45,11 +45,14 @@
 (struct story   (id user time body up down comments) #:transparent)
 (struct comment (id user body up down) #:transparent)        
 
-(:= (random-time) (- epoch (random 1000)))
+(:= users (vector "tim" "kat" "dave" "sally" "mitch" "walter" "george" "ingrid"))
+
 (:= (random-user) 
-  (:= users (vector "tim" "kat" "dave" "sally" "mitch" "walter" "george" "ingrid"))
    (vector-ref users (random (vector-length users))))
 
+(:= (random-time) 
+   (- epoch (random 1000)))
+
 (:= stories
     (for/list ((s 10))
       (story s (random-user) (random-time) "" (random 300) (random 100)
@@ -78,4 +81,4 @@
 (rank-comments (story-comments (list-ref stories 0)))
 
 (map (λ (s) (list (story-up s) (story-down s) (story-time s))) 
-     (rank-stories stories))
+     (rank-stories stories))
diff --git a/reddit-ranking.rkt b/reddit-ranking.rkt
@@ -0,0 +1,81 @@
+#lang racket
+(require "lite.rkt") 
+; https://raw.github.com/gist/2214946/7d16522c4feebae1745b7608801a5e5d4294b0c1/lite.rkt
+
+; Reddit ranking algorithms
+
+; Story ranking (hot ranking)
+; http://amix.dk/blog/post/19588
+; Submission time greatly affects score
+(:= epoch (current-seconds))
+
+(:= (hot upvotes downvotes date-seconds)
+
+  (:= time  (- date-seconds epoch))
+  (:= score (- upvotes downvotes))
+  (:= sign  (?? (> score 0)  1
+                (> score 0)  -1
+                             0))
+  (:= order (?? (< score 1)  1
+                             score))
+
+  (+ (log order) (/ (* sign time) 45000)))
+
+
+; Comment ranking (confidence sort using Wilson score)
+; http://www.evanmiller.org/how-not-to-sort-by-average-rating.html
+; Submission time doesn't affect score
+(:= (confidence upvotes downvotes)
+
+  (:= n (+ upvotes downvotes))
+
+  (?? (= n 0) 0
+
+      (let* ((z 1.0) ; 1.0 = 85%, 1.6 = 95% (sureness that comment will get to rank)
+             (z^2 (* z z))
+             (p (/ upvotes n)))
+
+        (real-part (/ (sqrt (- ; use minus for lower bound
+                             (+ p (/ z^2 (* 2 n))) 
+                             (* z (/ (+ (* p (- 1 p)) (/ z^2 (* 4 n)) n)))))
+                      (+ 1 (/ z^2 n)))))))
+
+
+; generating test data
+(struct story   (id user time body up down comments) #:transparent)
+(struct comment (id user body up down) #:transparent)        
+
+(:= (random-time) (- epoch (random 1000)))
+(:= (random-user) 
+  (:= users (vector "tim" "kat" "dave" "sally" "mitch" "walter" "george" "ingrid"))
+   (vector-ref users (random (vector-length users))))
+
+(:= stories
+    (for/list ((s 10))
+      (story s (random-user) (random-time) "" (random 300) (random 100)
+             (for/list ((c 10)) 
+               (comment c (random-user) "" (random 20) (random 20))))))
+
+
+; applying ranking
+(:= ((comparing f) x y) 
+  (> (f x) (f y)))
+
+(:= (story-heat story)
+  (hot (story-up story) (story-down story) (story-time story)))
+
+(:= (comment-confidence comment)
+  (confidence (comment-up comment) (comment-down comment)))
+
+(:= (rank-stories stories) 
+  (sort stories (comparing story-heat)))
+
+(:= (rank-comments comments)
+  (sort comments (comparing comment-confidence)))
+
+
+; try it out
+(rank-comments (story-comments (list-ref stories 0)))
+
+(map (λ (s) (list (story-up s) (story-down s) (story-time s))) 
+     (rank-stories stories))