From 8875b420a873a360a9484778b487394add318a5e Mon Sep 17 00:00:00 2001
From: wukong <wukong@longaeva>
Date: Wed, 13 Jun 2018 21:41:39 -0700
Subject: added shebang, replaced if-elses with shortcut notation, ported
 online mean and variance calc to mean.awk

---
 mean.awk | 37 +++++++++++++++++++++++++++++--------
 1 file changed, 29 insertions(+), 8 deletions(-)

(limited to 'mean.awk')

diff --git a/mean.awk b/mean.awk
index 45bedee..c1d31a6 100644
--- a/mean.awk
+++ b/mean.awk
@@ -1,13 +1,34 @@
+#!/usr/bin/awk -f
+
 ### mean.awk
-# find mean average of a list of numbers.
+# calculate mean average
 
 BEGIN {
-    X = ARGV[1]
-    inputsize = split(X, Xarr)
-    Yarr[n] = 0
-    SUM = 0
-    for (m=1; m <= inputsize; m++) {
-        SUM =+ Xarr[m]
+    sign = "[+-±]?"
+    decimal = "[0-9]+[.]?[0-9]*"
+    fraction = "[.][0-9]*"
+    exponent = "([Ee]" sign "[0-9]+)?"
+    number = "^" sign "(" decimal "|" fraction ")" exponent "$"
+}
+
+# Welford's 'online' algorithm for variance
+NF > 0 {
+    for (m=1; m<=NF; m++) {
+        if (m ~ number) {
+            count += 1
+            delta0 = $m - mean
+            mean = mean + delta0/count
+            delta1 = $m - mean
+            M2 = M2 + delta0*delta1
+            if (count > 1)
+                var = M2/(count - 1)
+            else
+                var = "nan"
+        }
     }
-    print SUM
+}
+
+END {
+    print "mean", "std_dev", "std_err", "count"
+    print mean, sqrt(var), sqrt(var/count), count
 }
-- 
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