Class LongMean

java.lang.Object
org.apache.commons.statistics.descriptive.LongMean
All Implemented Interfaces:
DoubleSupplier, IntSupplier, LongConsumer, LongSupplier, LongStatistic, StatisticAccumulator<LongMean>, StatisticResult
public final class LongMean extends Object implements LongStatistic, StatisticAccumulator<LongMean>
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

  • Field Details

    • SMALL_SUM

      private static final long SMALL_SUM
      Limit where the absolute sum can exactly map to a double. Set to 2^53.
      See Also:

    • sum

      private final Int128 sum
      Sum of the values.

    • n

      private long n
      Count of values that have been added.

  • Constructor Details

    • LongMean

      private LongMean()
      Create an instance.

    • LongMean

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

  • Method Details

    • create

      public static LongMean create()
      Creates an instance.

      The initial result is NaN.

      Returns:
      IntMean instance.

    • of

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

    • accept

      public void accept(long value)
      Updates the state of the statistic to reflect the addition of value.
      Specified by:
      accept in interface LongConsumer
      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 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

    • combine

      public LongMean combine(LongMean other)
      Description copied from interface: StatisticAccumulator
      Combines the state of the other statistic into this one.
      Specified by:
      combine in interface StatisticAccumulator<LongMean>
      Parameters:
      other - Another statistic to be combined.
      Returns:
      this instance after combining other.