From 0701902122308f376dab4f2a4371600ddc05ae3e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Lindqvist?= <bjourne@gmail.com>
Date: Sun, 15 Jan 2017 21:27:55 +0100
Subject: [PATCH] math.statistics: fix calculation of the harmonic mean

---
 basis/math/statistics/statistics-docs.factor  | 5 +++--
 basis/math/statistics/statistics-tests.factor | 5 ++++-
 basis/math/statistics/statistics.factor       | 2 +-
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/basis/math/statistics/statistics-docs.factor b/basis/math/statistics/statistics-docs.factor
index 83cb371978..04ed406463 100644
--- a/basis/math/statistics/statistics-docs.factor
+++ b/basis/math/statistics/statistics-docs.factor
@@ -12,7 +12,7 @@ HELP: harmonic-mean
 { $values { "seq" sequence } { "x" "a non-negative real number" } }
 { $description "Computes the harmonic mean of the elements in " { $snippet "seq" } ". The harmonic mean is appropriate when the average of rates is desired." }
 { $notes "Positive reals only." }
-{ $examples { $example "USING: math.statistics prettyprint ;" "{ 1 2 3 } harmonic-mean ." "6/11" } }
+{ $examples { $example "USING: math.statistics prettyprint ;" "{ 1 2 3 } harmonic-mean ." "18/11" } }
 { $errors "Throws a " { $link signal-error. } " (divide by zero) if the sequence is empty." } ;
 
 HELP: kth-smallest
@@ -24,7 +24,8 @@ HELP: mean
 { $values { "seq" sequence } { "x" "a non-negative real number" } }
 { $description "Computes the arithmetic mean of the elements in " { $snippet "seq" } "." }
 { $examples { $example "USING: math.statistics prettyprint ;" "{ 1 2 3 } mean ." "2" } }
-{ $errors "Throws a " { $link signal-error. } " (divide by zero) if the sequence is empty." } ;
+{ $errors "Throws a " { $link signal-error. } " (divide by zero) if the sequence is empty." }
+{ $see-also geometric-mean harmonic-mean } ;
 
 HELP: median
 { $values { "seq" sequence } { "x" "a non-negative real number" } }
diff --git a/basis/math/statistics/statistics-tests.factor b/basis/math/statistics/statistics-tests.factor
index 8b2d5ea305..8602a3148e 100644
--- a/basis/math/statistics/statistics-tests.factor
+++ b/basis/math/statistics/statistics-tests.factor
@@ -13,7 +13,10 @@ IN: math.statistics.tests
 { 1.0 } [ { 1 1 1 } geometric-mean ] unit-test
 { t } [ 1000 1000 <array> geometric-mean 1000 .01 ~ ] unit-test
 { t } [ 100000 100000 <array> geometric-mean 100000 .01 ~ ] unit-test
-{ 1/3 } [ { 1 1 1 } harmonic-mean ] unit-test
+
+{ 1 } [ { 1 1 1 } harmonic-mean ] unit-test
+{ 12/7 } [ { 1 2 4 } harmonic-mean ] unit-test
+
 { 5+1/4 } [ { 1 3 5 7 } contraharmonic-mean ] unit-test
 { 18 } [ { 4 8 15 16 23 42 } 0 trimmed-mean ] unit-test
 { 15+1/2 } [ { 4 8 15 16 23 42 } 0.2 trimmed-mean ] unit-test
diff --git a/basis/math/statistics/statistics.factor b/basis/math/statistics/statistics.factor
index fe18d0c855..15693f999f 100644
--- a/basis/math/statistics/statistics.factor
+++ b/basis/math/statistics/statistics.factor
@@ -35,7 +35,7 @@ IN: math.statistics
     [ [ log ] map-sum ] [ length ] bi /f e^ ; inline
 
 : harmonic-mean ( seq -- x )
-    [ recip ] map-sum recip ; inline
+    [ [ recip ] map-sum ] [ length swap / ] bi ; inline
 
 : contraharmonic-mean ( seq -- x )
     [ sum-of-squares ] [ sum ] bi / ; inline