Class Stats

  • All Implemented Interfaces:
    java.io.Serializable

    @Beta
    @GwtIncompatible
    public final class Stats
    extends java.lang.Object
    implements java.io.Serializable
    A bundle of statistical summary values -- sum, count, mean/average, min and max, and several forms of variance -- that were computed from a single set of zero or more floating-point values.

    There are two ways to obtain a Stats instance:

    • If all the values you want to summarize are already known, use the appropriate Stats.of factory method below. Primitive arrays, iterables and iterators of any kind of Number, and primitive varargs are supported.
    • Or, to avoid storing up all the data first, create a StatsAccumulator instance, feed values to it as you get them, then call StatsAccumulator.snapshot().

    Static convenience methods called meanOf are also provided for users who wish to calculate only the mean.

    Java 8 users: If you are not using any of the variance statistics, you may wish to use built-in JDK libraries instead of this class.

    Since:
    20.0
    Author:
    Pete Gillin, Kevin Bourrillion
    See Also:
    Serialized Form
    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      long count()
      Returns the number of values.
      boolean equals​(java.lang.Object obj)
      static Stats fromByteArray​(byte[] byteArray)
      Creates a Stats instance from the given byte representation which was obtained by toByteArray().
      int hashCode()
      double max()
      Returns the highest value in the dataset.
      double mean()
      Returns the arithmetic mean of the values.
      static double meanOf​(double... values)
      Returns the arithmetic mean of the values.
      static double meanOf​(int... values)
      Returns the arithmetic mean of the values.
      static double meanOf​(long... values)
      Returns the arithmetic mean of the values.
      static double meanOf​(java.lang.Iterable<? extends java.lang.Number> values)
      Returns the arithmetic mean of the values.
      static double meanOf​(java.util.Iterator<? extends java.lang.Number> values)
      Returns the arithmetic mean of the values.
      double min()
      Returns the lowest value in the dataset.
      static Stats of​(double... values)
      Returns statistics over a dataset containing the given values.
      static Stats of​(int... values)
      Returns statistics over a dataset containing the given values.
      static Stats of​(long... values)
      Returns statistics over a dataset containing the given values.
      static Stats of​(java.lang.Iterable<? extends java.lang.Number> values)
      Returns statistics over a dataset containing the given values.
      static Stats of​(java.util.Iterator<? extends java.lang.Number> values)
      Returns statistics over a dataset containing the given values.
      static Stats of​(java.util.stream.DoubleStream values)
      Returns statistics over a dataset containing the given values.
      static Stats of​(java.util.stream.IntStream values)
      Returns statistics over a dataset containing the given values.
      static Stats of​(java.util.stream.LongStream values)
      Returns statistics over a dataset containing the given values.
      double populationStandardDeviation()
      Returns the population standard deviation of the values.
      double populationVariance()
      Returns the population variance of the values.
      double sampleStandardDeviation()
      Returns the corrected sample standard deviation of the values.
      double sampleVariance()
      Returns the unbiased sample variance of the values.
      double sum()
      Returns the sum of the values.
      byte[] toByteArray()
      Gets a byte array representation of this instance.
      static java.util.stream.Collector<java.lang.Number,​StatsAccumulator,​Stats> toStats()
      Returns a Collector which accumulates statistics from a Stream of any type of boxed Number into a Stats.
      java.lang.String toString()  
      • Methods inherited from class java.lang.Object

        clone, finalize, getClass, notify, notifyAll, wait, wait, wait
    • Method Detail

      • of

        public static Stats of​(java.lang.Iterable<? extends java.lang.Number> values)
        Returns statistics over a dataset containing the given values.
        Parameters:
        values - a series of values, which will be converted to double values (this may cause loss of precision)
      • of

        public static Stats of​(java.util.Iterator<? extends java.lang.Number> values)
        Returns statistics over a dataset containing the given values. The iterator will be completely consumed by this method.
        Parameters:
        values - a series of values, which will be converted to double values (this may cause loss of precision)
      • of

        public static Stats of​(double... values)
        Returns statistics over a dataset containing the given values.
        Parameters:
        values - a series of values
      • of

        public static Stats of​(int... values)
        Returns statistics over a dataset containing the given values.
        Parameters:
        values - a series of values
      • of

        public static Stats of​(long... values)
        Returns statistics over a dataset containing the given values.
        Parameters:
        values - a series of values, which will be converted to double values (this may cause loss of precision for longs of magnitude over 2^53 (slightly over 9e15))
      • of

        public static Stats of​(java.util.stream.DoubleStream values)
        Returns statistics over a dataset containing the given values. The stream will be completely consumed by this method.

        If you have a Stream<Double> rather than a DoubleStream, you should collect the values using toStats() instead.

        Parameters:
        values - a series of values
        Since:
        28.2
      • of

        public static Stats of​(java.util.stream.IntStream values)
        Returns statistics over a dataset containing the given values. The stream will be completely consumed by this method.

        If you have a Stream<Integer> rather than an IntStream, you should collect the values using toStats() instead.

        Parameters:
        values - a series of values
        Since:
        28.2
      • of

        public static Stats of​(java.util.stream.LongStream values)
        Returns statistics over a dataset containing the given values. The stream will be completely consumed by this method.

        If you have a Stream<Long> rather than a LongStream, you should collect the values using toStats() instead.

        Parameters:
        values - a series of values, which will be converted to double values (this may cause loss of precision for longs of magnitude over 2^53 (slightly over 9e15))
        Since:
        28.2
      • toStats

        public static java.util.stream.Collector<java.lang.Number,​StatsAccumulator,​StatstoStats()
        Returns a Collector which accumulates statistics from a Stream of any type of boxed Number into a Stats. Use by calling boxedNumericStream.collect(toStats()). The numbers will be converted to double values (which may cause loss of precision).

        If you have any of the primitive streams DoubleStream, IntStream, or LongStream, you should use the factory method of(java.lang.Iterable<? extends java.lang.Number>) instead.

        Since:
        28.2
      • count

        public long count()
        Returns the number of values.
      • mean

        public double mean()
        Returns the arithmetic mean of the values. The count must be non-zero.

        If these values are a sample drawn from a population, this is also an unbiased estimator of the arithmetic mean of the population.

        Non-finite values

        If the dataset contains Double.NaN then the result is Double.NaN. If it contains both Double.POSITIVE_INFINITY and Double.NEGATIVE_INFINITY then the result is Double.NaN. If it contains Double.POSITIVE_INFINITY and finite values only or Double.POSITIVE_INFINITY only, the result is Double.POSITIVE_INFINITY. If it contains Double.NEGATIVE_INFINITY and finite values only or Double.NEGATIVE_INFINITY only, the result is Double.NEGATIVE_INFINITY.

        If you only want to calculate the mean, use meanOf(java.lang.Iterable<? extends java.lang.Number>) instead of creating a Stats instance.

        Throws:
        java.lang.IllegalStateException - if the dataset is empty
      • sum

        public double sum()
        Returns the sum of the values.

        Non-finite values

        If the dataset contains Double.NaN then the result is Double.NaN. If it contains both Double.POSITIVE_INFINITY and Double.NEGATIVE_INFINITY then the result is Double.NaN. If it contains Double.POSITIVE_INFINITY and finite values only or Double.POSITIVE_INFINITY only, the result is Double.POSITIVE_INFINITY. If it contains Double.NEGATIVE_INFINITY and finite values only or Double.NEGATIVE_INFINITY only, the result is Double.NEGATIVE_INFINITY.

      • populationVariance

        public double populationVariance()
        Returns the population variance of the values. The count must be non-zero.

        This is guaranteed to return zero if the dataset contains only exactly one finite value. It is not guaranteed to return zero when the dataset consists of the same value multiple times, due to numerical errors. However, it is guaranteed never to return a negative result.

        Non-finite values

        If the dataset contains any non-finite values (Double.POSITIVE_INFINITY, Double.NEGATIVE_INFINITY, or Double.NaN) then the result is Double.NaN.

        Throws:
        java.lang.IllegalStateException - if the dataset is empty
      • populationStandardDeviation

        public double populationStandardDeviation()
        Returns the population standard deviation of the values. The count must be non-zero.

        This is guaranteed to return zero if the dataset contains only exactly one finite value. It is not guaranteed to return zero when the dataset consists of the same value multiple times, due to numerical errors. However, it is guaranteed never to return a negative result.

        Non-finite values

        If the dataset contains any non-finite values (Double.POSITIVE_INFINITY, Double.NEGATIVE_INFINITY, or Double.NaN) then the result is Double.NaN.

        Throws:
        java.lang.IllegalStateException - if the dataset is empty
      • sampleVariance

        public double sampleVariance()
        Returns the unbiased sample variance of the values. If this dataset is a sample drawn from a population, this is an unbiased estimator of the population variance of the population. The count must be greater than one.

        This is not guaranteed to return zero when the dataset consists of the same value multiple times, due to numerical errors. However, it is guaranteed never to return a negative result.

        Non-finite values

        If the dataset contains any non-finite values (Double.POSITIVE_INFINITY, Double.NEGATIVE_INFINITY, or Double.NaN) then the result is Double.NaN.

        Throws:
        java.lang.IllegalStateException - if the dataset is empty or contains a single value
      • sampleStandardDeviation

        public double sampleStandardDeviation()
        Returns the corrected sample standard deviation of the values. If this dataset is a sample drawn from a population, this is an estimator of the population standard deviation of the population which is less biased than populationStandardDeviation() (the unbiased estimator depends on the distribution). The count must be greater than one.

        This is not guaranteed to return zero when the dataset consists of the same value multiple times, due to numerical errors. However, it is guaranteed never to return a negative result.

        Non-finite values

        If the dataset contains any non-finite values (Double.POSITIVE_INFINITY, Double.NEGATIVE_INFINITY, or Double.NaN) then the result is Double.NaN.

        Throws:
        java.lang.IllegalStateException - if the dataset is empty or contains a single value
      • min

        public double min()
        Returns the lowest value in the dataset. The count must be non-zero.

        Non-finite values

        If the dataset contains Double.NaN then the result is Double.NaN. If it contains Double.NEGATIVE_INFINITY and not Double.NaN then the result is Double.NEGATIVE_INFINITY. If it contains Double.POSITIVE_INFINITY and finite values only then the result is the lowest finite value. If it contains Double.POSITIVE_INFINITY only then the result is Double.POSITIVE_INFINITY.

        Throws:
        java.lang.IllegalStateException - if the dataset is empty
      • max

        public double max()
        Returns the highest value in the dataset. The count must be non-zero.

        Non-finite values

        If the dataset contains Double.NaN then the result is Double.NaN. If it contains Double.POSITIVE_INFINITY and not Double.NaN then the result is Double.POSITIVE_INFINITY. If it contains Double.NEGATIVE_INFINITY and finite values only then the result is the highest finite value. If it contains Double.NEGATIVE_INFINITY only then the result is Double.NEGATIVE_INFINITY.

        Throws:
        java.lang.IllegalStateException - if the dataset is empty
      • equals

        public boolean equals​(@CheckForNull
                              java.lang.Object obj)

        Note: This tests exact equality of the calculated statistics, including the floating point values. Two instances are guaranteed to be considered equal if one is copied from the other using second = new StatsAccumulator().addAll(first).snapshot(), if both were obtained by calling snapshot() on the same StatsAccumulator without adding any values in between the two calls, or if one is obtained from the other after round-tripping through java serialization. However, floating point rounding errors mean that it may be false for some instances where the statistics are mathematically equal, including instances constructed from the same values in a different order... or (in the general case) even in the same order. (It is guaranteed to return true for instances constructed from the same values in the same order if strictfp is in effect, or if the system architecture guarantees strictfp-like semantics.)

        Overrides:
        equals in class java.lang.Object
      • hashCode

        public int hashCode()

        Note: This hash code is consistent with exact equality of the calculated statistics, including the floating point values. See the note on equals(java.lang.Object) for details.

        Overrides:
        hashCode in class java.lang.Object
      • toString

        public java.lang.String toString()
        Overrides:
        toString in class java.lang.Object
      • meanOf

        public static double meanOf​(java.lang.Iterable<? extends java.lang.Number> values)
        Returns the arithmetic mean of the values. The count must be non-zero.

        The definition of the mean is the same as mean.

        Parameters:
        values - a series of values, which will be converted to double values (this may cause loss of precision)
        Throws:
        java.lang.IllegalArgumentException - if the dataset is empty
      • meanOf

        public static double meanOf​(java.util.Iterator<? extends java.lang.Number> values)
        Returns the arithmetic mean of the values. The count must be non-zero.

        The definition of the mean is the same as mean.

        Parameters:
        values - a series of values, which will be converted to double values (this may cause loss of precision)
        Throws:
        java.lang.IllegalArgumentException - if the dataset is empty
      • meanOf

        public static double meanOf​(double... values)
        Returns the arithmetic mean of the values. The count must be non-zero.

        The definition of the mean is the same as mean.

        Parameters:
        values - a series of values
        Throws:
        java.lang.IllegalArgumentException - if the dataset is empty
      • meanOf

        public static double meanOf​(int... values)
        Returns the arithmetic mean of the values. The count must be non-zero.

        The definition of the mean is the same as mean.

        Parameters:
        values - a series of values
        Throws:
        java.lang.IllegalArgumentException - if the dataset is empty
      • meanOf

        public static double meanOf​(long... values)
        Returns the arithmetic mean of the values. The count must be non-zero.

        The definition of the mean is the same as mean.

        Parameters:
        values - a series of values, which will be converted to double values (this may cause loss of precision for longs of magnitude over 2^53 (slightly over 9e15))
        Throws:
        java.lang.IllegalArgumentException - if the dataset is empty
      • toByteArray

        public byte[] toByteArray()
        Gets a byte array representation of this instance.

        Note: No guarantees are made regarding stability of the representation between versions.

      • fromByteArray

        public static Stats fromByteArray​(byte[] byteArray)
        Creates a Stats instance from the given byte representation which was obtained by toByteArray().

        Note: No guarantees are made regarding stability of the representation between versions.