utils.java

MacroWeka扩展了著名数据挖掘工具weka

   * be null. Any options accepted by the object will be removed from the
   * array.
   * @return the newly created object, ready for use.
   * @exception Exception if the class name is invalid, or if the
   * class is not assignable to the desired class type, or the options
   * supplied are not acceptable to the object
   */
  public static Object forName(Class classType,
			       String className,
			       String [] options) throws Exception {

    Class c = null;
    try {
      c = Class.forName(className);
    } catch (Exception ex) {
      throw new Exception("Can't find class called: " + className);
    }
    if (!classType.isAssignableFrom(c)) {
      throw new Exception(classType.getName() + " is not assignable from "
			  + className);
    }
    Object o = c.newInstance();
    if ((o instanceof OptionHandler)
	&& (options != null)) {
      ((OptionHandler)o).setOptions(options);
      Utils.checkForRemainingOptions(options);
    }
    return o;
  }

  /**
   * Computes entropy for an array of integers.
   *
   * @param counts array of counts
   * @return - a log2 a - b log2 b - c log2 c + (a+b+c) log2 (a+b+c)
   * when given array [a b c]
   */
  public static /*@pure@*/ double info(int counts[]) {
    
    int total = 0; int c;
    double x = 0;
    for (int j = 0; j < counts.length; j++) {
      x -= xlogx(counts[j]);
      total += counts[j];
    }
    return x + xlogx(total);
  }

  /**
   * Tests if a is smaller or equal to b.
   *
   * @param a a double
   * @param b a double
   */
  public static /*@pure@*/ boolean smOrEq(double a,double b) {
    
    return (a-b < SMALL);
  }

  /**
   * Tests if a is greater or equal to b.
   *
   * @param a a double
   * @param b a double
   */
  public static /*@pure@*/ boolean grOrEq(double a,double b) {
    
    return (b-a < SMALL);
  }
  
  /**
   * Tests if a is smaller than b.
   *
   * @param a a double
   * @param b a double
   */
  public static /*@pure@*/ boolean sm(double a,double b) {
    
    return (b-a > SMALL);
  }

  /**
   * Tests if a is greater than b.
   *
   * @param a a double
   * @param b a double 
   */
  public static /*@pure@*/ boolean gr(double a,double b) {
    
    return (a-b > SMALL);
  }

  /**
   * Returns the kth-smallest value in the array.
   *
   * @param array the array of integers
   * @param k the value of k
   * @return the kth-smallest value
   */
  public static double kthSmallestValue(int[] array, int k) {

    int [] index = new int[array.length];
    
    for (int i = 0; i < index.length; i++) {
      index[i] = i;
    }

    return array[index[select(array, index, 0, array.length - 1, k)]];
  }

  /**
   * Returns the kth-smallest value in the array
   *
   * @param array the array of double
   * @param k the value of k
   * @return the kth-smallest value
   */
  public static double kthSmallestValue(double[] array, int k) {

    int [] index = new int[array.length];
    
    for (int i = 0; i < index.length; i++) {
      index[i] = i;
    }

    return array[index[select(array, index, 0, array.length - 1, k)]];
  }

  /**
   * Returns the logarithm of a for base 2.
   *
   * @param a a double
   */
  public static /*@pure@*/ double log2(double a) {
    
    return Math.log(a) / log2;
  }

  /**
   * Returns index of maximum element in a given
   * array of doubles. First maximum is returned.
   *
   * @param doubles the array of doubles
   * @return the index of the maximum element
   */
  public static /*@pure@*/ int maxIndex(double [] doubles) {

    double maximum = 0;
    int maxIndex = 0;

    for (int i = 0; i < doubles.length; i++) {
      if ((i == 0) || (doubles[i] > maximum)) {
	maxIndex = i;
	maximum = doubles[i];
      }
    }

    return maxIndex;
  }

  /**
   * Returns index of maximum element in a given
   * array of integers. First maximum is returned.
   *
   * @param ints the array of integers
   * @return the index of the maximum element
   */
  public static /*@pure@*/ int maxIndex(int [] ints) {

    int maximum = 0;
    int maxIndex = 0;

    for (int i = 0; i < ints.length; i++) {
      if ((i == 0) || (ints[i] > maximum)) {
	maxIndex = i;
	maximum = ints[i];
      }
    }

    return maxIndex;
  }

  /**
   * Computes the mean for an array of doubles.
   *
   * @param vector the array
   * @return the mean
   */
  public static /*@pure@*/ double mean(double[] vector) {
  
    double sum = 0;

    if (vector.length == 0) {
      return 0;
    }
    for (int i = 0; i < vector.length; i++) {
      sum += vector[i];
    }
    return sum / (double) vector.length;
  }

  /**
   * Returns index of minimum element in a given
   * array of integers. First minimum is returned.
   *
   * @param ints the array of integers
   * @return the index of the minimum element
   */
  public static /*@pure@*/ int minIndex(int [] ints) {

    int minimum = 0;
    int minIndex = 0;

    for (int i = 0; i < ints.length; i++) {
      if ((i == 0) || (ints[i] < minimum)) {
	minIndex = i;
	minimum = ints[i];
      }
    }

    return minIndex;
  }

  /**
   * Returns index of minimum element in a given
   * array of doubles. First minimum is returned.
   *
   * @param doubles the array of doubles
   * @return the index of the minimum element
   */
  public static /*@pure@*/ int minIndex(double [] doubles) {

    double minimum = 0;
    int minIndex = 0;

    for (int i = 0; i < doubles.length; i++) {
      if ((i == 0) || (doubles[i] < minimum)) {
	minIndex = i;
	minimum = doubles[i];
      }
    }

    return minIndex;
  }

  /**
   * Normalizes the doubles in the array by their sum.
   *
   * @param doubles the array of double
   * @exception IllegalArgumentException if sum is Zero or NaN
   */
  public static void normalize(double[] doubles) {

    double sum = 0;
    for (int i = 0; i < doubles.length; i++) {
      sum += doubles[i];
    }
    normalize(doubles, sum);
  }

  /**
   * Normalizes the doubles in the array using the given value.
   *
   * @param doubles the array of double
   * @param sum the value by which the doubles are to be normalized
   * @exception IllegalArgumentException if sum is zero or NaN
   */
  public static void normalize(double[] doubles, double sum) {

    if (Double.isNaN(sum)) {
      throw new IllegalArgumentException("Can't normalize array. Sum is NaN.");
    }
    if (sum == 0) {
      // Maybe this should just be a return.
      throw new IllegalArgumentException("Can't normalize array. Sum is zero.");
    }
    for (int i = 0; i < doubles.length; i++) {
      doubles[i] /= sum;
    }
  }

  /**
   * Converts an array containing the natural logarithms of
   * probabilities stored in a vector back into probabilities.
   * The probabilities are assumed to sum to one.
   *
   * @param a an array holding the natural logarithms of the probabilities
   * @return the converted array 
   */
  public static double[] logs2probs(double[] a) {

    double max = a[maxIndex(a)];
    double sum = 0.0;

    double[] result = new double[a.length];
    for(int i = 0; i < a.length; i++) {
      result[i] = Math.exp(a[i] - max);
      sum += result[i];
    }

    normalize(result, sum);

    return result;
  } 

  /**
   * Rounds a double to the next nearest integer value. The JDK version
   * of it doesn't work properly.
   *
   * @param value the double value
   * @return the resulting integer value
   */
  public static /*@pure@*/ int round(double value) {

    int roundedValue = value > 0
      ? (int)(value + 0.5)
      : -(int)(Math.abs(value) + 0.5);
    
    return roundedValue;
  }

  /**
   * Rounds a double to the next nearest integer value in a probabilistic
   * fashion (e.g. 0.8 has a 20% chance of being rounded down to 0 and a
   * 80% chance of being rounded up to 1). In the limit, the average of
   * the rounded numbers generated by this procedure should converge to
   * the original double.
   *
   * @param value the double value
   * @return the resulting integer value
   */
  public static int probRound(double value, Random rand) {

    if (value >= 0) {
      double lower = Math.floor(value);
      double prob = value - lower;
      if (rand.nextDouble() < prob) {
	return (int)lower + 1;
      } else {
	return (int)lower;
      }
    } else {
      double lower = Math.floor(Math.abs(value));
      double prob = Math.abs(value) - lower;
      if (rand.nextDouble() < prob) {
	return -((int)lower + 1);
      } else {
	return -(int)lower;
      }
    }
  }

  /**
   * Rounds a double to the given number of decimal places.
   *
   * @param value the double value
   * @param afterDecimalPoint the number of digits after the decimal point
   * @return the double rounded to the given precision
   */
  public static /*@pure@*/ double roundDouble(double value,int afterDecimalPoint) {

    double mask = Math.pow(10.0, (double)afterDecimalPoint);

    return (double)(Math.round(value * mask)) / mask;
  }

  /**
   * Sorts a given array of integers in ascending order and returns an 
   * array of integers with the positions of the elements of the original 
   * array in the sorted array. The sort is stable. (Equal elements remain
   * in their original order.)
   *
   * @param array this array is not changed by the method!
   * @return an array of integers with the positions in the sorted
   * array.
   */
  public static /*@pure@*/ int[] sort(int [] array) {

    int [] index = new int[array.length];
    int [] newIndex = new int[array.length];
    int [] helpIndex;
    int numEqual;
    
    for (int i = 0; i < index.length; i++) {
      index[i] = i;
    }
    quickSort(array, index, 0, array.length - 1);

    // Make sort stable
    int i = 0;
    while (i < index.length) {
      numEqual = 1;
      for (int j = i + 1; ((j < index.length)
			   && (array[index[i]] == array[index[j]]));
	   j++) {
	numEqual++;
      }
      if (numEqual > 1) {
	helpIndex = new int[numEqual];
	for (int j = 0; j < numEqual; j++) {
	  helpIndex[j] = i + j;
	}
	quickSort(index, helpIndex, 0, numEqual - 1);
	for (int j = 0; j < numEqual; j++) {
	  newIndex[i + j] = index[helpIndex[j]];
	}
	i += numEqual;
      } else {
	newIndex[i] = index[i];
	i++;
      }
    }
    return newIndex;
  }

  /**
   * Sorts a given array of doubles in ascending order and returns an
   * array of integers with the positions of the elements of the
   * original array in the sorted array. NOTE THESE CHANGES: the sort
   * is no longer stable and it doesn't use safe floating-point
   * comparisons anymore. Occurrences of Double.NaN are treated as 
   * Double.MAX_VALUE
   *
   * @param array this array is not changed by the method!
   * @return an array of integers with the positions in the sorted
   * array.  
   */
  public static /*@pure@*/ int[] sort(/*@non_null@*/ double [] array) {

    int [] index = new int[array.length];
    array = (double [])array.clone();
    for (int i = 0; i < index.length; i++) {
      index[i] = i;
      if (Double.isNaN(array[i])) {
        array[i] = Double.MAX_VALUE;
      }
    }
    quickSort(array, index, 0, array.length - 1);
    return index;
  }

  /**