Package org.apache.commons.statistics.descriptive

Class IntMean

  • All Implemented Interfaces:
    java.util.function.DoubleSupplier, java.util.function.IntConsumer, java.util.function.IntSupplier, java.util.function.LongSupplier, IntStatistic, StatisticAccumulator<IntMean>, StatisticResult
    public final class IntMean
extends java.lang.Object
implements IntStatistic, StatisticAccumulator<IntMean>
    Computes the arithmetic mean of the available values. Uses the following definition of the sample mean:

    \[ \frac{1}{n} \sum_{i=1}^n x_i \]

    where \( n \) is the number of samples.

    • The result is NaN if no values are added.

    This class uses an exact integer sum to compute the mean. Supports up to 263 (exclusive) observations. This implementation does not check for overflow of the count.

    This class is designed to work with (though does not require) streams.

    This implementation is not thread safe. If multiple threads access an instance of this class concurrently, and at least one of the threads invokes the accept or combine method, it must be synchronized externally.

    However, it is safe to use accept and combine as accumulator and combiner functions of Collector on a parallel stream, because the parallel implementation of Stream.collect() provides the necessary partitioning, isolation, and merging of results for safe and efficient parallel execution.

    Since:
    1.1
    See Also:
    Mean (Wikipedia)

    • Field Summary

      Fields 
      Modifier and Type Field Description
      private long n
      Count of values that have been added.
      private static long SMALL_N
      Limit for small sample size where the sum can exactly map to a double.
      private Int128 sum
      Sum of the values.

    • Constructor Summary

      Constructors 
      Modifier Constructor Description
      private IntMean()
      Create an instance.
      private IntMean​(Int128 sum, int n)
      Create an instance.

    • Method Summary

      All Methods Static Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      void accept​(int value)
      Updates the state of the statistic to reflect the addition of value.
      IntMean combine​(IntMean other)
      Combines the state of the other statistic into this one.
      (package private) static double computeMean​(Int128 sum, long n)
      Compute the mean.
      static IntMean create()
      Creates an instance.
      double getAsDouble()
      Gets the mean of all input values.
      static IntMean of​(int... values)
      Returns an instance populated using the input values.

      • Methods inherited from class java.lang.Object

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

      • Methods inherited from interface java.util.function.IntConsumer

        andThen

    • Field Detail

      • SMALL_N

        private static final long SMALL_N
        Limit for small sample size where the sum can exactly map to a double. This is conservatively set using 2^21 values of 2^31 (2^21 ~ 2 million).
        See Also:
        Constant Field Values

      • sum

        private final Int128 sum
        Sum of the values.

      • n

        private long n
        Count of values that have been added.

    • Constructor Detail

      • IntMean

        private IntMean()
        Create an instance.

      • IntMean

        private IntMean​(Int128 sum,
                int n)
        Create an instance.
        Parameters:
        sum - Sum of the values.
        n - Count of values that have been added.

    • Method Detail

      • create

        public static IntMean create()
        Creates an instance.

        The initial result is NaN.

        Returns:
        IntMean instance.

      • of

        public static IntMean of​(int... values)
        Returns an instance populated using the input values.
        Parameters:
        values - Values.
        Returns:
        IntMean instance.

      • accept

        public void accept​(int value)
        Updates the state of the statistic to reflect the addition of value.
        Specified by:
        accept in interface java.util.function.IntConsumer
        Parameters:
        value - Value.

      • getAsDouble

        public double getAsDouble()
        Gets the mean of all input values.

        When no values have been added, the result is NaN.

        Specified by:
        getAsDouble in interface java.util.function.DoubleSupplier
        Returns:
        mean of all values.

      • computeMean

        static double computeMean​(Int128 sum,
                          long n)
        Compute the mean.

        This is a helper method used in higher order moments.

        Parameters:
        sum - Sum of the values.
        n - Count of the values.
        Returns:
        the mean