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java.lang.Objectorg.apache.commons.math.stat.descriptive.AbstractUnivariateStatistic
org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic
org.apache.commons.math.stat.descriptive.moment.Mean
public class Mean
Computes the arithmetic mean of a set of values. Uses the definitional formula:
mean = sum(x_i) / n
where n is the number of observations.
When increment(double) is used to add data incrementally from a
stream of (unstored) values, the value of the statistic that
getResult() returns is computed using the following recursive
updating algorithm:
m = the first valuem = m + (new value - m) / (number of observations) If AbstractStorelessUnivariateStatistic.evaluate(double[]) is used to compute the mean of an array
of stored values, a two-pass, corrected algorithm is used, starting with
the definitional formula computed using the array of stored values and then
correcting this by adding the mean deviation of the data values from the
arithmetic mean. See, e.g. "Comparison of Several Algorithms for Computing
Sample Means and Variances," Robert F. Ling, Journal of the American
Statistical Association, Vol. 69, No. 348 (Dec., 1974), pp. 859-866.
Returns Double.NaN if the dataset is empty.
increment() or
clear() method, it must be synchronized externally.
| Field Summary | |
|---|---|
protected boolean |
incMoment
Determines whether or not this statistic can be incremented or cleared. |
protected FirstMoment |
moment
First moment on which this statistic is based. |
| Constructor Summary | |
|---|---|
Mean()
Constructs a Mean. |
|
Mean(FirstMoment m1)
Constructs a Mean with an External Moment. |
|
Mean(Mean original)
Copy constructor, creates a new Mean identical
to the original |
|
| Method Summary | |
|---|---|
void |
clear()
Clears the internal state of the Statistic |
Mean |
copy()
Returns a copy of the statistic with the same internal state. |
static void |
copy(Mean source,
Mean dest)
Copies source to dest. |
double |
evaluate(double[] values,
double[] weights)
Returns the weighted arithmetic mean of the entries in the input array. |
double |
evaluate(double[] values,
double[] weights,
int begin,
int length)
Returns the weighted arithmetic mean of the entries in the specified portion of the input array, or Double.NaN if the designated subarray
is empty. |
double |
evaluate(double[] values,
int begin,
int length)
Returns the arithmetic mean of the entries in the specified portion of the input array, or Double.NaN if the designated subarray
is empty. |
long |
getN()
Returns the number of values that have been added. |
double |
getResult()
Returns the current value of the Statistic. |
void |
increment(double d)
Updates the internal state of the statistic to reflect the addition of the new value. |
| Methods inherited from class org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic |
|---|
equals, evaluate, hashCode, incrementAll, incrementAll |
| Methods inherited from class org.apache.commons.math.stat.descriptive.AbstractUnivariateStatistic |
|---|
evaluate, getData, getDataRef, setData, setData, test, test |
| Methods inherited from class java.lang.Object |
|---|
clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait |
| Field Detail |
|---|
protected FirstMoment moment
protected boolean incMoment
Statistics based on (constructed from) external moments cannot be incremented or cleared.
| Constructor Detail |
|---|
public Mean()
public Mean(FirstMoment m1)
m1 - the momentpublic Mean(Mean original)
Mean identical
to the original
original - the Mean instance to copy| Method Detail |
|---|
public void increment(double d)
increment in interface StorelessUnivariateStatisticincrement in class AbstractStorelessUnivariateStatisticd - the new value.public void clear()
clear in interface StorelessUnivariateStatisticclear in class AbstractStorelessUnivariateStatisticpublic double getResult()
getResult in interface StorelessUnivariateStatisticgetResult in class AbstractStorelessUnivariateStatisticDouble.NaN if it
has been cleared or just instantiated.public long getN()
getN in interface StorelessUnivariateStatistic
public double evaluate(double[] values,
int begin,
int length)
Double.NaN if the designated subarray
is empty.
Throws IllegalArgumentException if the array is null.
See Mean for details on the computing algorithm.
evaluate in interface UnivariateStatisticevaluate in class AbstractStorelessUnivariateStatisticvalues - the input arraybegin - index of the first array element to includelength - the number of elements to include
IllegalArgumentException - if the array is null or the array index
parameters are not validUnivariateStatistic.evaluate(double[], int, int)
public double evaluate(double[] values,
double[] weights,
int begin,
int length)
Double.NaN if the designated subarray
is empty.
Throws IllegalArgumentException if either array is null.
See Mean for details on the computing algorithm. The two-pass algorithm
described above is used here, with weights applied in computing both the original
estimate and the correction factor.
Throws IllegalArgumentException if any of the following are true:
evaluate in interface WeightedEvaluationvalues - the input arrayweights - the weights arraybegin - index of the first array element to includelength - the number of elements to include
IllegalArgumentException - if the parameters are not valid
public double evaluate(double[] values,
double[] weights)
Throws IllegalArgumentException if either array is null.
See Mean for details on the computing algorithm. The two-pass algorithm
described above is used here, with weights applied in computing both the original
estimate and the correction factor.
Throws IllegalArgumentException if any of the following are true:
evaluate in interface WeightedEvaluationvalues - the input arrayweights - the weights array
IllegalArgumentException - if the parameters are not validpublic Mean copy()
copy in interface StorelessUnivariateStatisticcopy in interface UnivariateStatisticcopy in class AbstractStorelessUnivariateStatistic
public static void copy(Mean source,
Mean dest)
Neither source nor dest can be null.
source - Mean to copydest - Mean to copy to
NullPointerException - if either source or dest is null
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