Package org.apache.commons.statistics.descriptive

Class Median

  • public final class Median
extends java.lang.Object
    Returns the median of the available values.

    For values of length n, let k = n / 2:

    • The result is NaN if n = 0.
    • The result is values[k] if n is odd.
    • The result is (values[k - 1] + values[k]) / 2 if n is even.

    This implementation respects the ordering imposed by Double.compare(double, double) for NaN values. If a NaN occurs in the selected positions in the fully sorted values then the result is NaN.

    The NaNPolicy can be used to change the behaviour on NaN values.

    Instances of this class are immutable and thread-safe.

    Since:
    1.1
    See Also:
    with(NaNPolicy), Median (Wikipedia)

    • Constructor Summary

      Constructors 
      Modifier Constructor Description
      private Median​(boolean copy, NaNPolicy nanPolicy)  

    • Field Detail

      • DEFAULT

        private static final Median DEFAULT
        Default instance.

      • copy

        private final boolean copy
        Flag to indicate if the data should be copied.

      • nanPolicy

        private final NaNPolicy nanPolicy
        NaN policy for floating point data.

      • nanTransformer

        private final NaNTransformer nanTransformer
        Transformer for NaN data.

    • Constructor Detail

      • Median

        private Median​(boolean copy,
               NaNPolicy nanPolicy)
        Parameters:
        copy - Flag to indicate if the data should be copied.
        nanPolicy - NaN policy.

    • Method Detail

      • withDefaults

        public static Median withDefaults()
        Return a new instance with the default options.

        Note: The default options configure for processing in-place and including NaN values in the data. This is the most efficient mode and has the smallest memory consumption.

        Returns:
        the median implementation
        See Also:
        withCopy(boolean), with(NaNPolicy)

      • withCopy

        public Median withCopy​(boolean v)
        Return an instance with the configured copy behaviour. If false then the input array will be modified by the call to evaluate the median; otherwise the computation uses a copy of the data.
        Parameters:
        v - Value.
        Returns:
        an instance

      • with

        public Median with​(NaNPolicy v)
        Return an instance with the configured NaNPolicy.

        Note: This implementation respects the ordering imposed by Double.compare(double, double) for NaN values: NaN is considered greater than all other values, and all NaN values are equal. The NaNPolicy changes the computation of the statistic in the presence of NaN values.

        • NaNPolicy.INCLUDE: NaN values are moved to the end of the data; the size of the data includes the NaN values and the median will be NaN if any value used for median interpolation is NaN.
        • NaNPolicy.EXCLUDE: NaN values are moved to the end of the data; the size of the data excludes the NaN values and the median will never be NaN for non-zero size. If all data are NaN then the size is zero and the result is NaN.
        • NaNPolicy.ERROR: An exception is raised if the data contains NaN values.

        Note that the result is identical for all policies if no NaN values are present.

        Parameters:
        v - Value.
        Returns:
        an instance

      • evaluate

        public double evaluate​(double[] values)
        Evaluate the median.

        Note: This method may partially sort the input values if not configured to copy the input data.

        Parameters:
        values - Values.
        Returns:
        the median

      • evaluate

        public double evaluate​(int[] values)
        Evaluate the median.

        Note: This method may partially sort the input values if not configured to copy the input data.

        Parameters:
        values - Values.
        Returns:
        the median