From c4637b5d7933eb4ff50a3e1639497b98a4eedd37 Mon Sep 17 00:00:00 2001
From: John Benediktsson <mrjbq7@gmail.com>
Date: Wed, 7 Nov 2012 17:05:06 -0800
Subject: [PATCH] math.extras: adding unique-indices.

---
 extra/math/extras/extras-tests.factor |  5 +++++
 extra/math/extras/extras.factor       | 12 ++++++++----
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/extra/math/extras/extras-tests.factor b/extra/math/extras/extras-tests.factor
index d55c1494c1..192a67ff81 100644
--- a/extra/math/extras/extras-tests.factor
+++ b/extra/math/extras/extras-tests.factor
@@ -72,3 +72,8 @@ IN: math.extras.test
 { { 0 5 1 2 2 } } [
     { -10 10 2 2.5 3 } [ { 1 2 3 4 5 } search-sorted ] map
 ] unit-test
+
+{
+    { 1 2 3 4 }
+    { 0 1 0 0 2 3 }
+} [ { 1 2 1 1 3 4 } unique-indices ] unit-test
diff --git a/extra/math/extras/extras.factor b/extra/math/extras/extras.factor
index 22c22bbcac..ea97795a22 100644
--- a/extra/math/extras/extras.factor
+++ b/extra/math/extras/extras.factor
@@ -1,10 +1,11 @@
 ! Copyright (C) 2012 John Benediktsson
 ! See http://factorcode.org/license.txt for BSD license
 
-USING: assocs combinators.short-circuit fry grouping kernel
-locals math math.combinatorics math.constants math.functions
-math.order math.primes math.ranges math.statistics math.vectors
-memoize random sequences sequences.extras sorting ;
+USING: assocs assocs.extras combinators.short-circuit fry
+grouping kernel locals math math.combinatorics math.constants
+math.functions math.order math.primes math.ranges
+math.statistics math.vectors memoize random sequences
+sequences.extras sets sorting ;
 
 IN: math.extras
 
@@ -194,3 +195,6 @@ PRIVATE>
 
 : weighted-random ( histogram -- obj )
     unzip cum-sum [ last random ] [ search-sorted ] bi swap nth ;
+
+: unique-indices ( seq -- unique indices )
+    [ members ] keep over dup length iota H{ } zip-as '[ _ at ] map ;