added shebang, replaced if-elses with shortcut notation, ported online mean and variance calc to mean.awk

1 files changed, 29 insertions, 8 deletions

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

 }