Class LongSumOfSquares

java.lang.Object
org.apache.commons.statistics.descriptive.LongSumOfSquares
All Implemented Interfaces:
DoubleSupplier, IntSupplier, LongConsumer, LongSupplier, LongStatistic, StatisticAccumulator<LongSumOfSquares>, StatisticResult
public final class LongSumOfSquares extends Object implements LongStatistic, StatisticAccumulator<LongSumOfSquares>
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 192-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

  • Field Details

    • sumSq

      private final UInt192 sumSq
      Sum of the squared values.

  • Constructor Details

    • LongSumOfSquares

      private LongSumOfSquares()
      Create an instance.

    • LongSumOfSquares

      private LongSumOfSquares(UInt192 sumSq)
      Create an instance.
      Parameters:
      sumSq - Sum of the squared values.

  • Method Details

    • create

      public static LongSumOfSquares create()
      Creates an instance.

      The initial result is zero.

      Returns:
      LongSumOfSquares instance.

    • of

      public static LongSumOfSquares of(long... values)
      Returns an instance populated using the input values.

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

      Parameters:
      values - Values.
      Returns:
      LongSumOfSquares instance.

    • ofRange

      public static LongSumOfSquares ofRange(long[] 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:
      LongSumOfSquares instance.
      Throws:
      IndexOutOfBoundsException - if the sub-range is out of bounds
      Since:
      1.2

    • createFromRange

      static LongSumOfSquares createFromRange(long[] 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:
      LongSumOfSquares instance.

    • getSumOfSquares

      UInt192 getSumOfSquares()
      Gets the sum of squares.

      This is package private for use in IntStatistics.

      Returns:
      the sum of squares

    • 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.

    • getAsInt

      public int getAsInt()
      Gets the sum of squares of all input values.

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

      Warning: This will raise an ArithmeticException if the result is not within the range [0, 2^31).

      Specified by:
      getAsInt in interface IntSupplier
      Specified by:
      getAsInt in interface StatisticResult
      Returns:
      sum of all values.
      Throws:
      ArithmeticException - if the result overflows an int
      See Also:

    • getAsLong

      public long getAsLong()
      Gets the sum of squares of all input values.

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

      Warning: This will raise an ArithmeticException if the result is not within the range [0, 2^63).

      Specified by:
      getAsLong in interface LongSupplier
      Specified by:
      getAsLong in interface StatisticResult
      Returns:
      sum of all values.
      Throws:
      ArithmeticException - if the result overflows a long
      See Also:

    • 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

      public BigInteger getAsBigInteger()
      Gets the sum of squares of all input values.

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

      Specified by:
      getAsBigInteger in interface StatisticResult
      Returns:
      sum of squares of all values.

    • combine

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