From 93494bc8d94e6ba40c64aaf5d4d9b536dcd93bf3 Mon Sep 17 00:00:00 2001
From: Eric Schulte <schulte.eric@gmail.com>
Date: Tue, 16 Nov 2010 22:58:10 -0700
Subject: [PATCH] mean and standard deviation functions in util

---
 src/neural_net/k_means.clj | 2 --
 src/neural_net/util.clj    | 7 +++++++
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/src/neural_net/k_means.clj b/src/neural_net/k_means.clj
index b30342a..0924815 100644
--- a/src/neural_net/k_means.clj
+++ b/src/neural_net/k_means.clj
@@ -5,8 +5,6 @@
 
 (defn euclid-dist [a b] (sqrt (reduce + (map (comp #(* % %) -) a b))))
 
-(defn mean [lst] (if (empty? lst) 0 (/ (reduce + lst) (count lst))))
-
 (defn k-means-update
   "A single iteration of k-means clustering."  [centers samples]
   (reduce        ; reposition each center at the center of its samples
diff --git a/src/neural_net/util.clj b/src/neural_net/util.clj
index d5e8551..d5e7249 100644
--- a/src/neural_net/util.clj
+++ b/src/neural_net/util.clj
@@ -13,6 +13,13 @@
 
 (defn rand-weight [] (- (rand 2) 1))
 
+(defn mean [lst] (if (empty? lst) 0 (/ (reduce + lst) (count lst))))
+
+(defn stddev [lst]
+  (let [m (mean lst)]
+    (sqrt (/ (reduce + (map (fn [el] (expt (- m el) 2)) lst))
+             (dec (count lst))))))
+
 (defn rms-error "Collect the error from an epic"
   ([net epic] (rms-error net epic identity))
   ([net epic pull]
-- 
2.11.4.GIT