1 files changed, 56 insertions, 0 deletions
diff --git a/pkg/lists/average.cl b/pkg/lists/average.cl
new file mode 100644
index 00000000..d6d12b6e
--- /dev/null
+++ b/pkg/lists/average.cl
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+#{ AVERAGE -- Compute the average and standard deviation of a list of numbers.
+# Numeric input is via the standard input (one number per line).  The mean,
+# sigma, and number of samples are written to the standard output.
+#
+# By default (Average called with no arguments), the sample is taken
+# to be the set of numbers in the standard input when Average is run.  
+# Additional points can be added to or deleted from the sample by
+# rerunning Average with one of the following arguments:
+# 
+#	add - add points to the sample, recalculate mean and sigma
+#	sub - subtract points from the sample
+
+
+{
+	if ($nargs == 0)		# if no arguments, don't query
+	    opstring = "new_sample"
+	else
+	    opstring = option		# get parameter "option"
+
+
+	if (opstring == "add")		# add, subtract, or start over?
+	    addsub_flag = 1
+	else if (opstring == "sub" || opstring == "subtract")
+	    addsub_flag = -1
+	else {				# new sample (default)
+	    addsub_flag = 1
+	    n = 0			# number of points in sample
+	    sum = 0
+	    sumsqrs = 0
+	}
+
+
+	# Process data;  print mean, sigma, and the sample size on
+	# the standard output.
+
+	while (scan (data_value) != EOF)
+	    if (nscan() == 1 && data_value != INDEF) {
+		n += addsub_flag
+		sum += addsub_flag * data_value 
+		sumsqrs += addsub_flag * data_value * data_value
+	    }
+
+	if (n <= 0)
+	    print ("INDEF ", "INDEF ", n)
+	else if (n == 1)
+	    print (sum, "INDEF ", 1)
+	else {
+	    mean = sum / n
+	    variance = (n * sumsqrs - sum * sum) / (n * (n-1))
+	    if (variance < 0)		# possible with roundoff error
+		sigma = 0.0
+	    else
+		sigma = sqrt (variance)
+	    print (mean, sigma, n)
+	}
+}