LMS-1187 add stdev function

SVN: 12788

openbis/source/java/ch/systemsx/cisd/openbis/generic/client/web/server/calculator/StandardFunctions.java

@@ -119,13 +119,38 @@ public final class StandardFunctions
         List<Double> array = toDoubleArray(values);
         assertNotEmpty(array, "avg");
         double sum = 0.0;
-        for (Double value : array)
+        for (double value : array)
         {
             sum += value;
         }
         return sum / array.size();
     }
     
+    /**
+     * Calculates the standard deviation of the specified values. 
+     * Blank strings or <code>null</code> values in the list are ignored.
+     * 
+     * @throws NumberFormatException if an element can not be parsed as a floating-point number.
+     * @throws IllegalArgumentException if the list is empty.
+     */
+    public static Double stdev(List<Object> values)
+    {
+        List<Double> array = toDoubleArray(values);
+        assertNotEmpty(array, "stdev");
+        double s1 = 0.0;
+        double s2 = 0.0;
+        for (double value : array)
+        {
+            s1 += value;
+            s2 += value * value;
+        }
+        int n = array.size();
+        double m1 = s1 / n;
+        double m2 = s2 / n;
+        return Math.sqrt(Math.max(0, m2 - m1 * m1));
+    }
+    
+    
     /**
      * Calculates the median of the specified values. 
      * Blank strings or <code>null</code> values in the list are ignored.

openbis/sourceTest/java/ch/systemsx/cisd/openbis/generic/client/web/server/calculator/StandardFunctionsTest.java

@@ -20,6 +20,7 @@ import static ch.systemsx.cisd.openbis.generic.client.web.server.calculator.Stan
 import static ch.systemsx.cisd.openbis.generic.client.web.server.calculator.StandardFunctions.DOUBLE_DEFAULT_VALUE;
 import static ch.systemsx.cisd.openbis.generic.client.web.server.calculator.StandardFunctions.choose;
 import static ch.systemsx.cisd.openbis.generic.client.web.server.calculator.StandardFunctions.avg;
+import static ch.systemsx.cisd.openbis.generic.client.web.server.calculator.StandardFunctions.stdev;
 import static ch.systemsx.cisd.openbis.generic.client.web.server.calculator.StandardFunctions.median;
 import static ch.systemsx.cisd.openbis.generic.client.web.server.calculator.StandardFunctions.min;
 import static ch.systemsx.cisd.openbis.generic.client.web.server.calculator.StandardFunctions.max;
@@ -130,6 +131,31 @@ public class StandardFunctionsTest extends AssertJUnit
     
     @Test
     public void testAvg()
+    {
+        assertEquals(0.0, stdev(Arrays.<Object>asList(1.5)));
+        assertEquals(2.0, stdev(Arrays.<Object>asList(2, 4, 4, 4, 5, 5, 7, 9)));
+        assertEquals(0.0, stdev(Arrays.<Object>asList(null, 1)));
+        assertEquals(4.5, stdev(Arrays.<Object>asList(" ", 1, "10")));
+        try
+        {
+            stdev(Arrays.<Object>asList());
+            fail("IllegalArgumentException expected");
+        } catch (IllegalArgumentException ex)
+        {
+            assertEquals("Argument of function 'stdev' is an empty array.", ex.getMessage());
+        }
+        try
+        {
+            stdev(Arrays.<Object>asList("a"));
+            fail("NumberFormatException expected");
+        } catch (NumberFormatException ex)
+        {
+            // ignored
+        }
+    }
+    
+    @Test
+    public void testStdev()
     {
         assertEquals(1.5, avg(Arrays.<Object>asList(1.5)));
         assertEquals(5.0, avg(Arrays.<Object>asList(1, 4, 10)));