Added mapping functions to MathArrays.

These methods allow to map any univariate or bivariate function to
arrays.

This fixes several pull requests on github, but uses a generalized
mapping approach rather than specific api for each function (closes #6,
closes #7, closes #8).

src/changes/changes.xml

@@ -54,6 +54,10 @@ If the output is not quite correct, check for invisible trailing spaces!
     </release>
 
     <release version="4.0" date="XXXX-XX-XX" description="">
+      <action dev="luc" type="add" >
+        Added mapping functions to MathArrays. These methods allow to map
+        any univariate or bivariate functions to arrays.
+      </action>
       <action dev="tn" type="fix" issue="MATH-1240"> <!-- backported to 3.6 -->
         "KolmogorovSmirnovTest#ksSum(...)" returned wrong result in case the provided
         t-parameters was zero. This affected the calculation of "approximateP(...)" for

src/main/java/org/apache/commons/math4/util/MathArrays.java

@@ -25,6 +25,8 @@ import java.util.Comparator;
 import java.util.List;
 
 import org.apache.commons.math4.Field;
+import org.apache.commons.math4.analysis.BivariateFunction;
+import org.apache.commons.math4.analysis.UnivariateFunction;
 import org.apache.commons.math4.distribution.UniformIntegerDistribution;
 import org.apache.commons.math4.exception.DimensionMismatchException;
 import org.apache.commons.math4.exception.MathArithmeticException;
@@ -107,6 +109,75 @@ public class MathArrays {
         }
     }
 
+    /**
+     * Creates an array whose contents will be the element-by-element
+     * mapping of the function to argument.
+     *
+     * @param f function to map on elements
+     * @param a array of function parameters.
+     * @return a new array {@code r} where {@code r[i] = f(a[i])}.
+     * @since 4.0
+     */
+    public static double[] map(final UnivariateFunction f, final double[] a) {
+
+        final double[] result = new double[a.length];
+        for (int i = 0; i < result.length; ++i) {
+            result[i] = f.value(a[i]);
+        }
+
+        return result;
+
+    }
+
+    /**
+     * Creates an array whose contents will be the element-by-element
+     * mapping of the function to arguments.
+     *
+     * @param f function to map on elements
+     * @param a array of first parameters of the function.
+     * @param b array of second parameters of the function.
+     * @return a new array {@code r} where {@code r[i] = f(a[i], b[i])}.
+     * @throws DimensionMismatchException if the array lengths differ.
+     * @since 4.0
+     */
+    public static double[] map(final BivariateFunction f,
+                               final double[] a, final double[] b) {
+
+        if (a.length != b.length) {
+            throw new DimensionMismatchException(a.length, b.length);
+        }
+
+        final double[] result = new double[a.length];
+        for (int i = 0; i < result.length; ++i) {
+            result[i] = f.value(a[i], b[i]);
+        }
+
+        return result;
+
+    }
+
+    /**
+     * Creates an array whose contents will be the element-by-element
+     * mapping of the function to arguments.
+     *
+     * @param f function to map on elements
+     * @param a array of first parameters of the function.
+     * @param b fixed value for second function parameter.
+     * @return a new array {@code r} where {@code r[i] = f(a[i])}.
+     * @since 4.0
+     */
+    public static double[] map(final BivariateFunction f,
+                               final double[] a, final double b) {
+
+        final double[] result = new double[a.length];
+        for (int i = 0; i < result.length; ++i) {
+            result[i] = f.value(a[i], b);
+        }
+
+        return result;
+
+    }
+
     /**
      * Creates an array whose contents will be the element-by-element
      * addition of the arguments.

src/test/java/org/apache/commons/math4/util/MathArraysTest.java

@@ -16,6 +16,8 @@ package org.apache.commons.math4.util;
 import java.util.Arrays;
 
 import org.apache.commons.math4.TestUtils;
+import org.apache.commons.math4.analysis.function.Abs;
+import org.apache.commons.math4.analysis.function.Add;
 import org.apache.commons.math4.exception.DimensionMismatchException;
 import org.apache.commons.math4.exception.MathArithmeticException;
 import org.apache.commons.math4.exception.MathIllegalArgumentException;
@@ -74,7 +76,37 @@ public class MathArraysTest {
             Assert.assertEquals(correctScaled[i], test[i], 0);
         }
     }
-    
+
+    @Test
+    public void testMapUnivariate() {
+        final double[] expected = new double[] { 1, 2, 4, 8 };
+        final double[] observed =
+            MathArrays.map(new Abs(), new double[] { 1, -2, -4, 8});
+        TestUtils.assertEquals(expected, observed, 1.0e-15);
+    }
+
+    @Test
+    public void testMapBivariateTwoArrays() {
+        final double[] expected = new double[] { 1, 3, 6, 11 };
+        final double[] observed =
+            MathArrays.map(new Add(),
+                           new double[] { 1, 2, 4, 8}, new double[] { 0, 1, 2, 3});
+        TestUtils.assertEquals(expected, observed, 1.0e-15);
+    }
+
+    @Test
+    public void testMapBivariateOneArray() {
+        final double[] expected = new double[] { 3.5, 4.5, 6.5, 10.5 };
+        final double[] observed =
+            MathArrays.map(new Add(), new double[] { 1, 2, 4, 8}, 2.5);
+        TestUtils.assertEquals(expected, observed, 1.0e-15);
+    }
+
+    @Test(expected=DimensionMismatchException.class)
+    public void testMapBivariatePrecondition() {
+        MathArrays.map(new Add(), new double[3], new double[4]);
+    }
+
     @Test(expected=DimensionMismatchException.class)
     public void testEbeAddPrecondition() {
         MathArrays.ebeAdd(new double[3], new double[4]);