Re: [math] Added constructors taking sample data as arguments to enumerated real and integer distributions. JIRA: MATH-1287.

[Gilles]

Hi Phil,

On Tue, 10 Nov 2015 03:48:33 +0000 (UTC), pste...@apache.org wrote:
Repository: commons-math
Updated Branches:
  refs/heads/MATH_3_X 8aecb842d -> 430c7f456

Added constructors taking sample data as arguments to enumerated real
and integer distributions. JIRA: MATH-1287.


[...]


http://git-wip-us.apache.org/repos/asf/commons-math/blob/430c7f45/src/main/java/org/apache/commons/math3/distribution/EnumeratedRealDistribution.java

----------------------------------------------------------------------
diff --git

a/src/main/java/org/apache/commons/math3/distribution/EnumeratedRealDistribution.java

b/src/main/java/org/apache/commons/math3/distribution/EnumeratedRealDistribution.java
index 07b96bc..2edb375 100644
---

a/src/main/java/org/apache/commons/math3/distribution/EnumeratedRealDistribution.java
+++

b/src/main/java/org/apache/commons/math3/distribution/EnumeratedRealDistribution.java
@@ -17,7 +17,10 @@
 package org.apache.commons.math3.distribution;

 import java.util.ArrayList;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;

 import 
org.apache.commons.math3.exception.DimensionMismatchException;
 import org.apache.commons.math3.exception.MathArithmeticException;
@@ -51,7 +54,7 @@ public class EnumeratedRealDistribution extends
AbstractRealDistribution {
     protected final EnumeratedDistribution<Double> 
innerDistribution;

     /**
-     * Create a discrete distribution using the given probability
mass function
+     * Create a discrete real-valued distribution using the given
probability mass function
      * enumeration.
      * <p>
      * <b>Note:</b> this constructor will implicitly create an 
instance of
@@ -77,7 +80,7 @@ public class EnumeratedRealDistribution extends
AbstractRealDistribution {
     }

     /**
-     * Create a discrete distribution using the given random number
generator
+     * Create a discrete real-valued distribution using the given
random number generator
      * and probability mass function enumeration.
      *
      * @param rng random number generator.
@@ -95,17 +98,73 @@ public class EnumeratedRealDistribution extends
AbstractRealDistribution {
         throws DimensionMismatchException, NotPositiveException,
MathArithmeticException,
                NotFiniteNumberException, NotANumberException {
         super(rng);
+
+        innerDistribution = new EnumeratedDistribution<Double>(
+                rng, createDistribution(singletons, probabilities));
+    }
+
+    /**
+     * Create a discrete real-valued distribution from the input
data.  Values are assigned
+     * mass based on their frequency.
+     *
+     * @param rng random number generator used for sampling
+     * @param data input dataset
+     */
+    public EnumeratedRealDistribution(final RandomGenerator rng,
final double[] data) {
+        super(rng);
+        final Map<Double, Integer> dataMap = new HashMap<Double, 
Integer>();
+
+        for (double value : data) {
+            Integer count = dataMap.get(value);
+            if (count == null) {
+                count = new Integer(1);
+            } else {
+                count = new Integer(count.intValue() + 1);
+            }
+            dataMap.put(value, count);
+        }


I'd suggest that the code in the above loop be written in the following 
way:

            Integer count = dataMap.get(value);
            if (count == null) {
                count = 0;
            }
            dataMap.put(value, ++count);

I think that it is nicer-looking, but it should also be more efficient
than using the
  new Integer(i)
construct for -128 < i < 127.

Gilles

[...]


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