Package org.apache.commons.statistics.descriptive

Class IntSumOfSquares

  • All Implemented Interfaces:
    DoubleSupplier, IntConsumer, IntSupplier, LongSupplier, IntStatistic, StatisticAccumulator<IntSumOfSquares>, StatisticResult
    public final class IntSumOfSquares
extends Object
implements IntStatistic, StatisticAccumulator<IntSumOfSquares>
    Returns the sum of the squares of the available values. Uses the following definition:

    \[ \sum_{i=1}^n x_i^2 \]

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

    • The result is zero if no values are observed.

    The implementation uses an exact integer sum to compute the sum of squared values. The exact sum is returned using getAsBigInteger(). Methods that return int or long primitives will raise an exception if the result overflows.

    Note that the implementation does not use BigInteger arithmetic; for performance the sum is computed using primitives to create an unsigned 128-bit integer. Support is provided for at least 263 observations.

    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

    • Method Detail

      • create

        public static IntSumOfSquares create()
        Creates an instance.

        The initial result is zero.

        Returns:
        IntSumOfSquares instance.

      • of

        public static IntSumOfSquares of​(int... values)
        Returns an instance populated using the input values.

        When the input is an empty array, the result is zero.

        Parameters:
        values - Values.
        Returns:
        IntSumOfSquares instance.

      • ofRange

        public static IntSumOfSquares ofRange​(int[] values,
                                      int from,
                                      int to)
        Returns an instance populated using the specified range of values.

        When the range is empty, the result is zero.

        Parameters:
        values - Values.
        from - Inclusive start of the range.
        to - Exclusive end of the range.
        Returns:
        IntSumOfSquares instance.
        Throws:
        IndexOutOfBoundsException - if the sub-range is out of bounds
        Since:
        1.2

      • accept

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

      • getAsDouble

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

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

        Note that this conversion can lose information about the precision of the BigInteger value.

        Specified by:
        getAsDouble in interface DoubleSupplier
        Returns:
        sum of squares of all values.
        See Also:
        getAsBigInteger()