metron-analytics/metron-statistics/src/test/java/org/apache/metron/statistics/informationtheory/EntropyTest.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
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 */
package org.apache.metron.statistics.informationtheory;

import org.junit.jupiter.api.Test;

import java.util.HashMap;

import static org.apache.metron.stellar.common.utils.StellarProcessorUtils.run;
import static org.junit.jupiter.api.Assertions.assertEquals;

public class EntropyTest {
  @Test
  public void entropyTest() {
    //test empty collection
    assertEquals(0.0, (Double) run("IT_ENTROPY({})", new HashMap<>()), 0.0);

    /*
    Now consider the string aaaaaaaaaabbbbbccccc or 10 a's followed by 5 b's and 5 c's.
    The probabilities of each character is as follows:
    p(a) = 1/2
    p(b) = 1/4
    p(c) = 1/4
    so the shannon entropy should be
      -p(a)*log_2(p(a)) - p(b)*log_2(p(b)) - p(c)*log_2(p(c)) =
      -0.5*-1 - 0.25*-2 - 0.25*-2 = 1.5
     */
    assertEquals(1.5, (Double) run("IT_ENTROPY({ 'a' : 10, 'b' : 5, 'c' : 5} )", new HashMap<>()), 0.0);
  }
}