movingGeometricMeanBy()

Calculate the moving geometric mean of BigDecimal objects mapped from a Stream<INPUT> via a mappingFunction.

Implementation Notes

This implementation is suitable for mapping an arbitrary Stream<INPUT> to BigDecimal via a mappingFunction; for a version that operates directly on a Stream<BigDecimal>, see movingGeometricMean(). 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).

Signatures

movingGeometricMeanBy(int windowSize, Function<INPUT, BigDecimal> mappingFunction)

windowSize - How many trailing elements to calculate the geometric mean over
mappingFunction - A non-null function to map stream INPUT elements into BigDecimal for calculation

Additional Methods

Method	Purpose
`excludePartialValues()`	When calculating the moving geometric mean, and the full size of the window has not yet been reached, the gatherer should suppress emitting values until the lookback window is full. See example.
`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 it only makes sense in a very narrow set of circumstances.

Examples

Moving geometric mean, mapped from an object

record NamedValue(String name, BigDecimal value) {}

Stream
    .of(
        new NamedValue("first",  BigDecimal.valueOf(1)),
        new NamedValue("second", BigDecimal.valueOf(8)),
        new NamedValue("third",  BigDecimal.valueOf(64))
    )
    .gather(Gatherers4j.movingGeometricMeanBy(2, NamedValue::value))
    .toList();

// [ 
//   BigDecimal("1"), 
//   BigDecimal("2.828427124746190"),
//   BigDecimal("22.62741699796952") 
// ]

Excluding partial values

Showing that in-process moving geometric mean values are not emitted for each element until the lookback window has been filled.

record NamedValue(String name, BigDecimal value) {}

Stream
    .of(
        new NamedValue("first",  BigDecimal.valueOf(1)),
        new NamedValue("second", BigDecimal.valueOf(8)),
        new NamedValue("third",  BigDecimal.valueOf(64))
    )
    .gather(Gatherers4j.movingGeometricMeanBy(2, NamedValue::value).excludePartialValues())
    .toList();

// [ 
//   BigDecimal("2.828427124746190"),
//   BigDecimal("22.62741699796952") 
// ]

Showing nulls are ignored by default

record NamedValue(String name, BigDecimal value) {}

Stream
    .of(
        new NamedValue("first",  null),
        new NamedValue("second", BigDecimal.valueOf(1)),
        new NamedValue("third",  BigDecimal.valueOf(8)),
        new NamedValue("fourth", BigDecimal.valueOf(64))
    )
    .gather(Gatherers4j.movingGeometricMeanBy(2, NamedValue::value))
    .toList();

// [
//   BigDecimal("1"), 
//   BigDecimal("2.828427124746190"), 
//   BigDecimal("22.62741699796952") 
// ]

Treating null as one

record NamedValue(String name, BigDecimal value) {}

Stream
    .of(
        new NamedValue("first",  null),
        new NamedValue("second", BigDecimal.valueOf(1)),
        new NamedValue("third",  BigDecimal.valueOf(8))
    )
    .gather(Gatherers4j.movingGeometricMeanBy(2, NamedValue::value).treatNullAsOne())
    .toList();

// [
//   BigDecimal("1"),
//   BigDecimal("1"),
//   BigDecimal("2.828427124746190")
// ]

Replacing null with another `BigDecimal`

record NamedValue(String name, BigDecimal value) {}

Stream
    .of(
        new NamedValue("first",  null),
        new NamedValue("second", BigDecimal.valueOf(1)),
        new NamedValue("third",  BigDecimal.valueOf(8))
    )
    .gather(Gatherers4j.movingGeometricMeanBy(2, NamedValue::value).treatNullAs(BigDecimal.valueOf(27)))
    .toList();

// [
//   BigDecimal("27"),
//   BigDecimal("5.196152422706632"),
//   BigDecimal("2.828427124746190") 
// ]

Specifying a new `MathContext`

record NamedValue(String name, BigDecimal value) {}

Stream
    .of(
        new NamedValue("first",  BigDecimal.valueOf(1)),
        new NamedValue("second", BigDecimal.valueOf(8))
    )
    .gather(Gatherers4j
        .movingGeometricMeanBy(2, NamedValue::value)
        .withMathContext(new MathContext(2))
    )
    .toList();

// [ 
//   BigDecimal("1.0"), 
//   BigDecimal("2.8")
// ]

Emitting a record containing the original and calculated values

record NamedValue(String name, BigDecimal value) {}

Stream
    .of(
        new NamedValue("first",  BigDecimal.valueOf(1)),
        new NamedValue("second", BigDecimal.valueOf(8))
    )
    .gather(Gatherers4j.movingGeometricMeanBy(2, NamedValue::value).withOriginal())
    .toList();

// [ 
//   WithOriginal[original=NamedValue[name=first, value=1], calculated=1],
//   WithOriginal[original=NamedValue[name=second, value=8], calculated=2.828427124746190]
// ]