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java.lang.Objectuaa.feral.util.Statistics
public class Statistics
A number of static methods to compute statistical properties of an
array of double values.
Implements the computation of mean, variance and standard deviation
for double
values.
Method Summary | |
---|---|
static double[] |
combineData(double[] values1,
double[] values2)
|
static double |
computeMean(double[] values)
Computes the mean value for the argument array. |
static double |
computeMean(double[] values,
int offset,
int number)
Computes the mean value for some elements of the argument array. |
static double |
computeMedian(double[] a,
int from,
int to)
Find the median value of the specified interval of the argument array. |
static double |
computeStandardDeviation(double[] values)
Computes the standard deviation for the argument array of values. |
static double |
computeStandardDeviation(double[] values,
double mean)
Computes the standard deviation for the argument array of values. |
static double |
computeStandardDeviation(double[] values,
int offset,
int number)
Computes the standard deviation for some of the argument array's values. |
static double |
computeStandardDeviation(double[] values,
int offset,
int number,
double mean)
Computes the standard deviation for some of the argument array's values. |
static double |
computeSum(double[] values)
Method to compute the sum of a double array. |
static double |
computeSum(int[] values)
Method to compute the sum of a double array. |
static double |
computeVariance(double[] values)
Computes the variance for the argument array. |
static double |
computeVariance(double[] values,
double mean)
Computes the variance for some of the argument array's values. |
static double |
computeVariance(double[] values,
int offset,
int number)
Computes the variance for some of the argument array's values. |
static double |
computeVariance(double[] values,
int offset,
int number,
double mean)
Computes the variance for some of the argument array's values. |
static void |
swap(double[] a,
int i1,
int i2)
Exchange two elements in the argument array. |
Methods inherited from class java.lang.Object |
---|
equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Method Detail |
---|
public static double computeMean(double[] values)
values
- double array on which the mean is to be determined
java.lang.IllegalArgumentException
- if the array has not at least one elementpublic static double computeMean(double[] values, int offset, int number)
values
- array from which elements are readoffset
- index of the first element to be usednumber
- number of elements to be used
java.lang.IllegalArgumentException
- if the array has not at least one elementpublic static double computeSum(double[] values)
values
- the double array
public static double computeSum(int[] values)
values
- the double array
public static double computeStandardDeviation(double[] values)
values
- array from which elements are read
java.lang.IllegalArgumentException
- if the array has not at least two elementspublic static double computeStandardDeviation(double[] values, double mean)
values
- array from which elements are readmean
- the mean value for the array, possibly computed with a
call to computeMean(double[])
.
java.lang.IllegalArgumentException
- if the array has not at least two elementspublic static double computeStandardDeviation(double[] values, int offset, int number)
computeMean(double[], int, int)
,
better call computeStandardDeviation(double[], int, int, double)
.
Otherwise, this method has to compute mean again.
values
- array from which elements are readoffset
- first element to be usednumber
- number of elements used starting at values[offset]
java.lang.IllegalArgumentException
- if the array has not at least two elementspublic static double computeStandardDeviation(double[] values, int offset, int number, double mean)
values
- array from which elements are readoffset
- first element to be usednumber
- number of elements used starting at values[offset]mean
- value of the elements
java.lang.IllegalArgumentException
- if the array has not at least two elementspublic static double computeVariance(double[] values)
values
- array from which elements are read
java.lang.IllegalArgumentException
- if the array has not at least two elementspublic static double computeVariance(double[] values, double mean)
values
- array from which elements are readmean
- the mean for the array elements
java.lang.IllegalArgumentException
- if the array has not at least two elementspublic static double computeVariance(double[] values, int offset, int number)
computeMean(double[], int, int)
,
better call computeVariance(double[], int, int, double)
.
Otherwise, this method has to compute mean again.
values
- array from which elements are readoffset
- first element to be usednumber
- number of elements used starting at values[offset]
java.lang.IllegalArgumentException
- if the array has not at least two elementspublic static double computeVariance(double[] values, int offset, int number, double mean)
values
- array from which elements are readoffset
- first element to be usednumber
- number of elements used starting at values[offset]mean
- the mean for the array elements
java.lang.IllegalArgumentException
- if the array has not at least two elementspublic static double[] combineData(double[] values1, double[] values2)
public static void swap(double[] a, int i1, int i2)
a
- the array in which two elements are swappedi1
- index of the first elementi2
- index of the second element
java.lang.ArrayIndexOutOfBoundsException
- if either i1 or i2 are
not valid index values into a (from 0 to a.length - 1)public static double computeMedian(double[] a, int from, int to)
from
and goes to
to
; the values at these positions are included.
Note that the array will be modified while searching, so you might want
to backup your data.
This implementation is a port of the C function from
quickselect.c
, provided at http://ndevilla.free.fr/median/.
The page is a good resource for various median value algorithms, including
implementations and benchmarks.
The original code on which this class is based was written in C++ by Martin Leese. It was ported to C and optimized by Nicolas Devillard (author of the above mentioned page). The algorithm is from Numerical recipes in C, Second Edition, Cambridge University Press, 1992, Section 8.5, ISBN 0-521-43108-5.
a
- the arrayfrom
- the index of the start of the interval in which the median value will be searchedto
- the index of the end of the interval in which the median value will be searched
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