cern.jet.stat.quantile
Class EquiDepthHistogram

java.lang.Object
  cern.colt.PersistentObject
      cern.jet.stat.quantile.EquiDepthHistogram

All Implemented Interfaces:

Cloneable, Serializable

public class EquiDepthHistogram

extends PersistentObject

Read-only equi-depth histogram for selectivity estimation. Assume you have collected statistics over a data set, among them a one-dimensional equi-depth histogram (quantiles). Then an applications or DBMS might want to estimate the selectivity of some range query [from,to], i.e. the percentage of data set elements contained in the query range. This class does not collect equi-depth histograms but only space efficiently stores already produced histograms and provides operations for selectivity estimation. Uses linear interpolation.

This class stores a list l of float values for which holds:

Let v be a list of values (sorted ascending) an equi-depth histogram has been computed over.

Let s=l.length.

Let p=(0, 1/s-1), 2/s-1,..., s-1/s-1=1.0) be a list of the s percentages.

Then for each i=0..s-1: l[i] = e : v.contains(e) && v[0],..., v[p[i]*v.length] <= e.

(In particular: l[0]=min(v)=v[0] and l[s-1]=max(v)=v[s-1].)

Version:

1.0, 09/24/99

See Also:

Serialized Form

Field Summary

Fields inherited from class cern.colt.PersistentObject

serialVersionUID

Constructor Summary

EquiDepthHistogram(float[] quantileElements)
Constructs an equi-depth histogram with the given quantile elements.

Method Summary

int	binOfElement(float element) Returns the bin index of the given element.
int	bins() Returns the number of bins.
float	endOfBin(int binIndex) Returns the end of the range associated with the given bin.
double	percentFromTo(float from, float to) Returns the percentage of elements in the range (from,to].
double	phi(float element) Returns how many percent of the elements contained in the receiver are <= element.
int	size() Deprecated. Deprecated. Returns the number of bin boundaries.
float	startOfBin(int binIndex) Returns the start of the range associated with the given bin.
static void	test(float element) Not yet commented.

Methods inherited from class cern.colt.PersistentObject

clone

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

EquiDepthHistogram

public EquiDepthHistogram(float[] quantileElements)

Constructs an equi-depth histogram with the given quantile elements. Quantile elements must be sorted ascending and have the form specified in the class documentation.

Method Detail

binOfElement

public int binOfElement(float element)

Returns the bin index of the given element. In other words, returns a handle to the range the element falls into.

Parameters:

element - the element to search for.

Throws:

IllegalArgumentException - if the element is not contained in any bin.

bins

public int bins()

Returns the number of bins. In other words, returns the number of subdomains partitioning the entire value domain.

endOfBin

public float endOfBin(int binIndex)

Returns the end of the range associated with the given bin.

Throws:

ArrayIndexOutOfBoundsException - if binIndex < 0 || binIndex >= bins().

percentFromTo

public double percentFromTo(float from,
                            float to)

Returns the percentage of elements in the range (from,to]. Does linear interpolation.

Parameters:

from - the start point (exclusive).

to - the end point (inclusive).

phi

public double phi(float element)

Returns how many percent of the elements contained in the receiver are <= element. Does linear interpolation.

size

public int size()

Deprecated. Deprecated. Returns the number of bin boundaries.

startOfBin

public float startOfBin(int binIndex)

Returns the start of the range associated with the given bin.

Throws:

ArrayIndexOutOfBoundsException - if binIndex < 0 || binIndex >= bins().

test

public static void test(float element)

Not yet commented.