From 35bd1a4bbc5ccc0e12e3312bfbadc4ce99638234 Mon Sep 17 00:00:00 2001
From: John Benediktsson <mrjbq7@gmail.com>
Date: Wed, 26 Sep 2012 15:11:41 -0700
Subject: [PATCH] math.extras: invent "cum-reduce" concept for gini.

---
 extra/math/extras/extras.factor | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/extra/math/extras/extras.factor b/extra/math/extras/extras.factor
index d8ee57d69d..bdc92c300b 100644
--- a/extra/math/extras/extras.factor
+++ b/extra/math/extras/extras.factor
@@ -155,15 +155,15 @@ PRIVATE>
 : until-zero ( n quot -- )
     [ dup zero? ] swap until drop ; inline
 
-: sum-cum-sum ( seq -- sum sum-of-cumulative-sum-of-seq )
-    [ 0 0 ] dip [ '[ _ + ] dip dupd + ] each ; inline
+: cum-reduce ( ... seq identity quot: ( ... prev elt -- ... next ) -- ... result cum-result )
+    [ dup rot ] dip dup '[ _ curry dip dupd @ ] each ; inline
 
 <PRIVATE
 
 :: (gini) ( seq -- x )
     seq natural-sort :> sorted
     seq length :> len
-    sorted sum-cum-sum :> ( a b )
+    sorted 0 [ + ] cum-reduce :> ( a b )
     b len a * / :> B
     1 len recip + 2 B * - ;