From e9ffd2da37d2dedff67a19afd96c8537a511bcbe Mon Sep 17 00:00:00 2001
From: John Benediktsson <mrjbq7@gmail.com>
Date: Thu, 12 Apr 2012 10:30:16 -0700
Subject: [PATCH] math.statistics: adding cumulative versions of sum, product,
 min, and max.

---
 basis/math/statistics/statistics-docs.factor  | 40 +++++++++++++++++++
 basis/math/statistics/statistics-tests.factor |  5 +++
 basis/math/statistics/statistics.factor       | 12 ++++++
 3 files changed, 57 insertions(+)

diff --git a/basis/math/statistics/statistics-docs.factor b/basis/math/statistics/statistics-docs.factor
index a86709c7be..129125d7c3 100644
--- a/basis/math/statistics/statistics-docs.factor
+++ b/basis/math/statistics/statistics-docs.factor
@@ -174,6 +174,46 @@ HELP: sequence>hashtable
     }
 } ;
 
+HELP: cum-sum
+{ $values { "seq" sequence } { "seq'" sequence } }
+{ $description "Returns the cumulative sum of " { $snippet "seq" } "." }
+{ $examples
+    { $example "USING: math.statistics prettyprint ;"
+               "{ 1 -1 2 -1 4 } cum-sum ."
+               "{ 1 0 2 1 5 }"
+    }
+} ;
+
+HELP: cum-product
+{ $values { "seq" sequence } { "seq'" sequence } }
+{ $description "Returns the cumulative product of " { $snippet "seq" } "." }
+{ $examples
+    { $example "USING: math.statistics prettyprint ;"
+               "{ 1 2 3 4 } cum-product ."
+               "{ 1 2 6 24 }"
+    }
+} ;
+
+HELP: cum-min
+{ $values { "seq" sequence } { "seq'" sequence } }
+{ $description "Returns the cumulative min of " { $snippet "seq" } "." }
+{ $examples
+    { $example "USING: math.statistics prettyprint ;"
+               "{ 5 3 4 1 } cum-min ."
+               "{ 5 3 3 1 }"
+    }
+} ;
+
+HELP: cum-max
+{ $values { "seq" sequence } { "seq'" sequence } }
+{ $description "Returns the cumulative max of " { $snippet "seq" } "." }
+{ $examples
+    { $example "USING: math.statistics prettyprint ;"
+               "{ 1 -1 3 5 } cum-max ."
+               "{ 1 1 3 5 }"
+    }
+} ;
+
 ARTICLE: "histogram" "Computing histograms"
 "Counting elements in a sequence:"
 { $subsections
diff --git a/basis/math/statistics/statistics-tests.factor b/basis/math/statistics/statistics-tests.factor
index 5b7606eab6..67323f0a41 100644
--- a/basis/math/statistics/statistics-tests.factor
+++ b/basis/math/statistics/statistics-tests.factor
@@ -71,3 +71,8 @@ IN: math.statistics.tests
 
 [ 1.0 ] [ { 1 2 3 } { 1 2 3 } corr ] unit-test
 [ -1.0 ] [ { 1 2 3 } { -4 -5 -6 } corr ] unit-test
+
+[ { 1 2 4 7 } ] [ { 1 1 2 3 } cum-sum ] unit-test
+[ { 1 1 2 6 } ] [ { 1 1 2 3 } cum-product ] unit-test
+[ { 5 3 3 1 } ] [ { 5 3 4 1 } cum-min ] unit-test
+[ { 1 3 3 5 } ] [ { 1 3 1 5 } cum-max ] unit-test
diff --git a/basis/math/statistics/statistics.factor b/basis/math/statistics/statistics.factor
index f14a2c3680..d0f203f5c7 100644
--- a/basis/math/statistics/statistics.factor
+++ b/basis/math/statistics/statistics.factor
@@ -156,3 +156,15 @@ ERROR: empty-sequence ;
 
 : corr ( {x} {y} -- corr )
      [ cov ] [ [ var ] bi@ * sqrt ] 2bi / ;
+
+: cum-sum ( seq -- seq' )
+    0 swap [ + dup ] map nip ;
+
+: cum-product ( seq -- seq' )
+    1 swap [ * dup ] map nip ;
+
+: cum-min ( seq -- seq' )
+    [ ?first ] keep [ min dup ] map nip ;
+
+: cum-max ( seq -- seq' )
+    [ ?first ] keep [ max dup ] map nip ;