Add convenience method for initialization

Author: DaGeRe

src/main/java/org/apache/commons/math4/stat/descriptive/SummaryStatistics.java

@@ -132,6 +132,26 @@ public SummaryStatistics(SummaryStatistics original) throws NullArgumentExceptio
         copy(original, this);
     }
 
+    /**
+     * Construct a SummaryStatistics instance filling it with the given initialDoubleArray
+     * @param initialDoubleArray values for filling the array
+     */
+    public SummaryStatistics(double[] initialDoubleArray) {
+        for (double initialValue : initialDoubleArray) {
+           addValue(initialValue);
+        }
+    }
+
+    /**
+     * Construct a SummaryStatistics instance filling it with the given initialDoubleArray
+     * @param initialDoubleArray values for filling the array
+     */
+    public SummaryStatistics(Double[] initialDoubleArray) {
+        for (Double initialValue : initialDoubleArray) {
+           addValue(initialValue);
+        }
+    }
+
     /**
      * Return a {@link StatisticalSummaryValues} instance reporting current
      * statistics.

src/test/java/org/apache/commons/math4/stat/descriptive/SummaryStatisticsTest.java

@@ -315,6 +315,9 @@ public void testQuadraticMean() {
         expected = Math.sqrt(expected);
 
         Assert.assertEquals(expected, stats.getQuadraticMean(), Math.ulp(expected));
+
+        SummaryStatistics convenienceMethodStatistics = new SummaryStatistics(values);
+        Assert.assertEquals(expected, convenienceMethodStatistics.getQuadraticMean(), Math.ulp(expected));	
     }
 
     /**