org.apache.commons.math3.stat.correlation

## Class KendallsCorrelation

- java.lang.Object
- - org.apache.commons.math3.stat.correlation.KendallsCorrelation

-     public class KendallsCorrelation
      extends Object

  Implementation of Kendall's Tau-b rank correlation.

  A pair of observations (x1, y1) and (x2, y2) are considered concordant if x1 < x2 and y1 < y2 or x2 < x1 and y2 < y1. The pair is discordant if x1 < x2 and y2 < y1 or x2 < x1 and y1 < y2. If either x1 = x2 or y1 = y2, the pair is neither concordant nor discordant.

  Kendall's Tau-b is defined as:

       taub = (nc - nd) / sqrt((n0 - n1) * (n0 - n2))

  where:

  - n0 = n * (n - 1) / 2
  - nc = Number of concordant pairs
  - nd = Number of discordant pairs
  - n1 = sum of ti * (ti - 1) / 2 for all i
  - n2 = sum of uj * (uj - 1) / 2 for all j
  - ti = Number of tied values in the ith group of ties in x
  - uj = Number of tied values in the jth group of ties in y

  This implementation uses the O(n log n) algorithm described in William R. Knight's 1966 paper "A Computer Method for Calculating Kendall's Tau with Ungrouped Data" in the Journal of the American Statistical Association.

  Since:
    3.3
  Version:
    $Id: KendallsCorrelation.java 1548907 2013-12-07 13:08:06Z tn $
  See Also:
    Kendall tau rank correlation coefficient (Wikipedia), A Computer Method for Calculating Kendall's Tau with Ungrouped Data

- - ### Constructor Summary

    Constructors
    Constructor and Description
    `KendallsCorrelation()` Create a KendallsCorrelation instance without data.
    `KendallsCorrelation(double[][] data)` Create a KendallsCorrelation from a rectangular array whose columns represent values of variables to be correlated.
    `KendallsCorrelation(RealMatrix matrix)` Create a KendallsCorrelation from a RealMatrix whose columns represent variables to be correlated.

  - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `RealMatrix` | `computeCorrelationMatrix(double[][] matrix)` Computes the Kendall's Tau rank correlation matrix for the columns of the input rectangular array.
    `RealMatrix` | `computeCorrelationMatrix(RealMatrix matrix)` Computes the Kendall's Tau rank correlation matrix for the columns of the input matrix.
    `double` | `correlation(double[] xArray, double[] yArray)` Computes the Kendall's Tau rank correlation coefficient between the two arrays.
    `RealMatrix` | `getCorrelationMatrix()` Returns the correlation matrix.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Constructor Detail

    - #### KendallsCorrelation

          public KendallsCorrelation()

      Create a KendallsCorrelation instance without data.

    - #### KendallsCorrelation

          public KendallsCorrelation(double[][] data)

      Create a KendallsCorrelation from a rectangular array whose columns represent values of variables to be correlated.
      Parameters:
        `data` - rectangular array with columns representing variables
      Throws:
        `IllegalArgumentException` - if the input data array is not rectangular with at least two rows and two columns.

    - #### KendallsCorrelation

          public KendallsCorrelation(RealMatrix matrix)

      Create a KendallsCorrelation from a RealMatrix whose columns represent variables to be correlated.
      Parameters:
        `matrix` - matrix with columns representing variables to correlate

  - ### Method Detail

    - #### getCorrelationMatrix

          public RealMatrix getCorrelationMatrix()

      Returns the correlation matrix.
      Returns:
        correlation matrix

    - #### computeCorrelationMatrix

          public RealMatrix computeCorrelationMatrix(RealMatrix matrix)

      Computes the Kendall's Tau rank correlation matrix for the columns of the input matrix.
      Parameters:
        `matrix` - matrix with columns representing variables to correlate
      Returns:
        correlation matrix

    - #### computeCorrelationMatrix

          public RealMatrix computeCorrelationMatrix(double[][] matrix)

      Computes the Kendall's Tau rank correlation matrix for the columns of the input rectangular array. The columns of the array represent values of variables to be correlated.
      Parameters:
        `matrix` - matrix with columns representing variables to correlate
      Returns:
        correlation matrix

    - #### correlation

          public double correlation(double[] xArray,
                           double[] yArray)
                             throws DimensionMismatchException

      Computes the Kendall's Tau rank correlation coefficient between the two arrays.
      Parameters:
        `xArray` - first data array
        `yArray` - second data array
      Returns:
        Returns Kendall's Tau rank correlation coefficient for the two arrays
      Throws:
        `DimensionMismatchException` - if the arrays lengths do not match

Copyright © 2003–2014 The Apache Software Foundation. All rights reserved.