runningHarmonicMean()

Calculate the running harmonic mean of a Stream<BigDecimal>.

Implementation Notes

This implementation is suitable for Stream<BigDecimal>. For a version that takes a user-specified mapping function, see runningHarmonicMeanBy(). By default, nulls are ignored and play no part in calculations, see treatNullAs() and treatNullAsOne() below for ways to change this behavior. The default MathContext for all calculations is MathContext.DECIMAL64, but this can be overridden (see withMathContext(), below).

A 0 anywhere in the stream is undefined for a harmonic mean and will throw an ArithmeticException. If the reciprocals of the values cancel out to zero instead, for example 1 and -1, the harmonic mean is undefined and nothing is emitted for that element.

Signatures

runningHarmonicMean()

Additional Methods

Method	Purpose
`treatNullAsOne()`	When encountering a `null` value in a stream, treat it as `BigDecimal.ONE` instead. See example.
`treatNullAs(BigDecimal replacement)`	When encountering a `null` value in a stream, treat it as the given `replacement` value instead. See example.
`withMathContext(MathContext mathContext)`	Replace the `MathContext` used for all mathematical operations performed by this gatherer. See example.
`withOriginal()`	Include the original input value from the stream in addition to the calculated value in a `WithOriginal` record. See example.

Note: treatNullAsZero() is also a valid method on this gatherer, but since 0 is undefined for a harmonic mean, it will cause an ArithmeticException as soon as a null value is encountered.

Examples

Running harmonic mean

Stream
    .of("1", "2", "4")
    .map(BigDecimal::new)
    .gather(Gatherers4j.runningHarmonicMean())
    .toList();

// [ 
//   BigDecimal("1"), 
//   BigDecimal("1.333333333333333"),
//   BigDecimal("1.714285714285714")
// ]

Showing nulls are ignored by default

Stream
    .of(BigDecimal.valueOf(2), null, BigDecimal.valueOf(8))
    .gather(Gatherers4j.runningHarmonicMean())
    .toList();

// [ 
//   BigDecimal("2"),
//   BigDecimal("3.2")
// ]

Treating null as one

Stream
    .of(BigDecimal.valueOf(2), null, BigDecimal.valueOf(8))
    .gather(Gatherers4j.runningHarmonicMean().treatNullAsOne())
    .toList();

// [ 
//   BigDecimal("2"),
//   BigDecimal("1.333333333333333"),
//   BigDecimal("1.846153846153846")
// ]

Replacing null with another `BigDecimal`

Stream
    .of(BigDecimal.valueOf(2), null, BigDecimal.valueOf(50))
    .gather(Gatherers4j.runningHarmonicMean().treatNullAs(BigDecimal.valueOf(8)))
    .toList();

// [  
//   BigDecimal("2"),  
//   BigDecimal("3.2"),  
//   BigDecimal("4.651162790697674") 
// ]

Specifying a new `MathContext`

Stream
    .of("1", "3")
    .map(BigDecimal::new)
    .gather(Gatherers4j
        .runningHarmonicMean()
        .withMathContext(new MathContext(2))
    )
    .toList();

// [ 
//   BigDecimal("1"), 
//   BigDecimal("1.5") 
// ]

Emitting a record containing the original and calculated values

Stream
    .of("1", "2", "4")
    .map(BigDecimal::new)
    .gather(Gatherers4j.runningHarmonicMean().withOriginal())
    .toList();

// [ 
//   WithOriginal[original=1, calculated=1],
//   WithOriginal[original=2, calculated=1.333333333333333],
//   WithOriginal[original=4, calculated=1.714285714285714]
// ]