Implementation of a simple training program in Python, Java and Scala

JTrain.java

// vim: set ts=4 sw=4 et:

import java.io.FileReader;
import java.io.BufferedReader;
import java.io.IOException;
import java.util.Iterator;
import java.util.Scanner;
import java.util.HashMap;
import java.util.Map;

public class JTrain {
    /** Keep track of feature frequencies. */
    static HashMap<String, int[]> counter = new HashMap<String, int[]>();

    public static void main(String[] args) throws IOException {
        Scanner train = null;
        try {
            train = new Scanner(
                    new BufferedReader(
                        new FileReader(args[0])));

            for (String token: Iter.string(train))
                if (!token.isEmpty()) {
                    boolean upper = Character.isUpperCase(token.charAt(0));
                    for (String feature: features(token.toLowerCase()))
                        count(feature, upper);
                }
        } finally {
            if (train != null)
                train.close();
        }

        for (Map.Entry<String, int[]> entry: counter.entrySet())
            System.out.printf("%s %d %d\n",
                    entry.getKey(),
                    entry.getValue()[0],
                    entry.getValue()[1]);
    }

    public static void count(String key, boolean upper) {
        int index = upper ? 1 : 0;
        if (!counter.containsKey(key)) {
            int[] v = {0, 0};
            counter.put(key, v);
        }
        //counter.get(key)[index]++;
        counter.get(key)[index] = roughCount(counter.get(key)[index]);
    }


    public static String[] features(String word) {
        String[] fs = {
            word,
            substring(word, 0, 2),
            substring(word, 0, 3),
            substring(word, -2, -1),
            substring(word, -3, -1),
        };
        return fs;
    }

    /**
     * Substring indexing similar to Python slices.
     */
    public static String substring(String s, int i, int j) {
        int n = s.length();
        i = i < 0 ? n + i: i;
        j = j < 0 ? n + 1 + j : j;
        return s.substring(Math.max(i, 0), Math.max(0, Math.min(j, n)));
    }

    /**
     * Probabilistic counting, catch every log(N) occurrences.
     */
    public static int roughCount(int value) {
        double n = Math.random();
        return (n < (1.0 / (1 << value))) ? value + 1 : value;
    }

    /**
     * Iterable wrapper around an Iterator object.
     */
    static class Iter<T> implements Iterable<T> {
        private Iterator<T> t = null;
        Iter (Iterator<T> t) {
            assert(t != null);
            this.t = t;
        }
        public Iterator<T> iterator() { return t; }
        public static Iterable<String> string(Iterator<String> t) { return new Iter<String>(t); }
    }
}

STrain.scala

object STrain {
  val rnd = new util.Random()
  val map = new collection.mutable.HashMap[String, Array[Int]]

  def main(args: Array[String]) {
    if (args.length > 0) {
      // Build the map of feature frequencies.
      for {
        line <- io.Source.fromFile(args(0)).getLines
        token <- line.split("[ \t]+") if !token.isEmpty
      } {
        val upper = token(0).isUpper
        for (feature <- features(token.toLowerCase))
             count(feature, upper)
      }
      // Print the resulting map.
      for ((key, value) <- map)
        println("%s %d %d".format(key, value(0), value(1)))
    } else
      Console.err.println("usage: STrain <filename>")
  }

  def count(key: String, upper: Boolean) = {
    val idx = if (upper) 1 else 0
    if (!map.contains(key))
      map += (key -> Array(0, 0))
    map(key)(idx) = roughCount(map(key)(idx))
  }

  def roughCount(value: Int) = {
    if (rnd.nextDouble() < 1.0 / (1 << value)) value + 1 else value
  }

  def features(word: String) = Array(
      word,
      slice(word, 0, 2),
      slice(word, 0, 3),
      slice(word,-2,-1),
      slice(word,-3,-1)
    )

  def slice(s: String, from: Int, upto: Int) = {
    val n = s.length
    val i = from + (if (from < 0) n else 0)
    val j = upto + (if (upto < 0) n + 1 else 0)
    s.slice(0 max i, 0 max (n min j))
  }
}

train.py

#!/usr/bin/env python

import sys, random
from collections import defaultdict

def main(args):
    if len(args) < 2:
        print "usage: %s <filename>" % args[0]
        return 1

    counts = defaultdict(lambda: [0, 0])
    def count(f, i):
        counts[f][i] = rough_count(counts[f][i])

    with open(args[1]) as f:
        for token in (t for line in f for t in line.split() if t):
            upper = token[0].isupper()
            for feature in features(token.lower()):
                count(feature, upper)

    for k, (l, u) in counts.iteritems():
        print "%s %d %d" % (k, l, u)

    return 0


def features(word):
    return word, word[-3:], word[:3], word[-2:], word[:2]

def rough_count(val):
    return val + 1 if random.random() < 1.0 / (1 << val)\
                   else val


if __name__ == '__main__':
    sys.exit(main(sys.argv))