Initial data commit

Task/Cumulative-standard-deviation/Crystal/cumulative-standard-deviation-1.crystal

@@ -0,0 +1,16 @@
+class StdDevAccumulator
+  def initialize
+    @n, @sum, @sum2 = 0, 0.0, 0.0
+  end
+
+  def <<(num)
+    @n += 1
+    @sum += num
+    @sum2 += num**2
+    Math.sqrt (@sum2 * @n - @sum**2) / @n**2
+  end
+end
+
+sd = StdDevAccumulator.new
+i = 0
+[2,4,4,4,5,5,7,9].each { |n| puts "adding #{n}: stddev of #{i+=1} samples is #{sd << n}" }

Task/Cumulative-standard-deviation/Crystal/cumulative-standard-deviation-2.crystal

@@ -0,0 +1,12 @@
+def sdaccum
+  n, sum, sum2 = 0, 0.0, 0.0
+  ->(num : Int32) do
+    n += 1
+    sum += num
+    sum2 += num**2
+    Math.sqrt( (sum2 * n - sum**2) / n**2 )
+  end
+end
+
+sd = sdaccum
+[2,4,4,4,5,5,7,9].each {|n| print sd.call(n), ", "}