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## 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.

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