Class SumOfSquares

java.lang.Object
org.apache.commons.statistics.descriptive.SumOfSquares
All Implemented Interfaces:
DoubleConsumer, DoubleSupplier, IntSupplier, LongSupplier, DoubleStatistic, StatisticAccumulator<SumOfSquares>, StatisticResult
public final class SumOfSquares extends Object implements DoubleStatistic, StatisticAccumulator<SumOfSquares>
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 result is NaN if any of the values is NaN.
  • The result is +infinity if any of the values is infinity, or the sum overflows.

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

This instance 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 instance of Stream.collect() provides the necessary partitioning, isolation, and merging of results for safe and efficient parallel execution.

Since:
1.1

  • Field Details

    • ss

      private double ss
      Sum of squares of all values.

  • Constructor Details

    • SumOfSquares

      private SumOfSquares()
      Create an instance.

  • Method Details

    • create

      public static SumOfSquares create()
      Creates an instance.

      The initial result is zero.

      Returns:
      SumOfSquares instance.

    • of

      public static SumOfSquares of(double... values)
      Returns an instance populated using the input values.

      The result is NaN if any of the values is NaN.

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

      Parameters:
      values - Values.
      Returns:
      SumOfSquares instance.

    • ofRange

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

      The result is NaN if any of the values is NaN.

      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:
      SumOfSquares instance.
      Throws:
      IndexOutOfBoundsException - if the sub-range is out of bounds
      Since:
      1.2

    • createFromRange

      static SumOfSquares createFromRange(double[] values, int from, int to)
      Create an instance using the specified range of values.

      Warning: No range checks are performed.

      Parameters:
      values - Values.
      from - Inclusive start of the range.
      to - Exclusive end of the range.
      Returns:
      SumOfSquares instance.

    • accept

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

      Specified by:
      getAsDouble in interface DoubleSupplier
      Returns:
      sum of squares of all values.

    • combine

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