Entropy/Narcissist: Difference between revisions

=={{header|Java}}==

<lang java>

import java.io.BufferedReader;

import java.io.File;

import java.io.FileReader;

import java.io.IOException;

import java.util.HashMap;

import java.util.Map;

public class EntropyNarcissist {

private static final String FILE_NAME = "src/EntropyNarcissist.java";

public static void main(String[] args) {

System.out.printf("Entropy of file \"%s\" = %.12f.%n", FILE_NAME, getEntropy(FILE_NAME));

}

private static double getEntropy(String fileName) {

Map<Character,Integer> characterCount = new HashMap<>();

int length = 0;

try (BufferedReader reader = new BufferedReader(new FileReader(new File(fileName)));) {

int c = 0;

while ( (c = reader.read()) != -1 ) {

characterCount.merge((char) c, 1, (v1, v2) -> v1 + v2);

length++;

}

}

catch ( IOException e ) {

throw new RuntimeException(e);

}

double entropy = 0;

for ( char key : characterCount.keySet() ) {

double fraction = (double) characterCount.get(key) / length;

entropy -= fraction * Math.log(fraction);

}

return entropy;

}

}

</lang>

{{out}}

<pre>Entropy of file "src/EntropyNarcissist.java" = 3.244796514218.

</pre>