Data commit

Task/Cumulative-standard-deviation/PHP/cumulative-standard-deviation.php

@@ -0,0 +1,31 @@
+<?php
+class sdcalc {
+    private  $cnt, $sumup, $square;
+
+    function __construct() {
+       $this->reset();
+    }
+    # callable on an instance
+    function reset() {
+       $this->cnt=0; $this->sumup=0; $this->square=0;
+    }
+    function add($f) {
+        $this->cnt++;
+        $this->sumup  += $f;
+        $this->square += pow($f, 2);
+        return $this->calc();
+    }
+    function calc() {
+        if ($this->cnt==0 || $this->sumup==0) {
+            return 0;
+        } else {
+            return sqrt($this->square / $this->cnt - pow(($this->sumup / $this->cnt),2));
+        }
+    }
+ }
+
+# start test, adding test data one by one
+$c = new sdcalc();
+foreach ([2,4,4,4,5,5,7,9] as $v) {
+    printf('Adding %g: result %g%s', $v, $c->add($v), PHP_EOL);
+}