Data commit

Task/Cumulative-standard-deviation/E/cumulative-standard-deviation-1.e

@@ -0,0 +1,24 @@
+def makeRunningStdDev() {
+    var sum := 0.0
+    var sumSquares := 0.0
+    var count := 0.0
+
+    def insert(v) {
+        sum += v
+        sumSquares += v ** 2
+        count += 1
+    }
+
+    /** Returns the standard deviation of the inputs so far, or null if there
+        have been no inputs. */
+    def stddev() {
+        if (count > 0) {
+            def meanSquares := sumSquares/count
+            def mean := sum/count
+            def variance := meanSquares - mean**2
+            return variance.sqrt()
+        }
+    }
+
+    return [insert, stddev]
+}

Task/Cumulative-standard-deviation/E/cumulative-standard-deviation-2.e

@@ -0,0 +1,18 @@
+? def [insert, stddev] := makeRunningStdDev()
+# value: <insert>, <stddev>
+
+? [stddev()]
+# value: [null]
+
+? for value in [2,4,4,4,5,5,7,9] {
+>     insert(value)
+>     println(stddev())
+> }
+0.0
+1.0
+0.9428090415820626
+0.8660254037844386
+0.9797958971132716
+1.0
+1.3997084244475297
+2.0