movingSum()

Calculate the moving sum of a Stream<BigDecimal> looking back windowSize number of elements.

Implementation Notes

This implementation is suitable for Stream<BigDecimal>, for a version that takes user-specified mapping function see movingSumBy(). By default, nulls are ignored and play no part in calculations, see treatNullAs() and treatNullAsZero() 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

movingSum(int windowSize)

windowSize - How many trailing elements to calculate the sum over

Additional Methods

Method	Purpose
`includePartialValues()`	When calculating the moving sum and the full size of the window has not yet been reached, the gatherer should emit values for what it has. See example.
`treatNullAsZero()`	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.

Examples

Moving sum of window size 3

Stream
    .of("1.0", "2.0", "10.0", "2.0")
    .map(BigDecimal::new)
    .gather(Gatherers4j.movingSum(3))
    .toList();

// [ 
//   BigDecimal("13.0"), 
//   BigDecimal("14.0") 
// ]

Including partial values

Showing that an in-process moving sum is emitted for each element, even if there aren’t 3 elements from which to calculate a full window yet.

Stream
    .of("1.0", "2.0", "10.0", "2.0")
    .map(BigDecimal::new)
    .gather(Gatherers4j.movingSum(3).includePartialValues())
    .toList();

// [ 
//   BigDecimal("1.0"), 
//   BigDecimal("3.0"), 
//   BigDecimal("13.0"), 
//   BigDecimal("14.0") 
// ]

Showing nulls are ignored by default

Stream
    .of(null, null, new BigDecimal("10.0"), new BigDecimal("2.0"), new BigDecimal("1.0"))
    .gather(Gatherers4j.movingSum(3))
    .toList();

// [  
//   BigDecimal("13.0")
// ]

Treating null as zero

Stream
    .of(null, null, new BigDecimal("10.0"), new BigDecimal("2.0"))
    .gather(Gatherers4j.movingSum(3).treatNullAsZero())
    .toList();

// [ 
//   BigDecimal("10.0"), 
//   BigDecimal("12.00") 
// ]

Replacing null with another `BigDecimal`

Stream
    .of(null, null, new BigDecimal("10.0"), new BigDecimal("2.0"))
    .gather(Gatherers4j.movingSum(3).treatNullAs(new BigDecimal("3.5")))
    .toList();

// [ 
//   BigDecimal("17.0"), 
//   BigDecimal("15.5") 
// ]

Specifying a new `MathContext`

Stream
    .of("1.111", "2.222", "10.333", "2.444")
    .map(BigDecimal::new)
    .gather(Gatherers4j
        .movingSum(3)
        .withMathContext(new MathContext(3, RoundingMode.DOWN))
    )
    .toList();

// [ 
//   BigDecimal("13.6"), 
//   BigDecimal("14.9") 
// ]

Emitting a record containing the original and calculated values

Stream
    .of("1.0", "2.0", "10.0", "2.0")
    .map(BigDecimal::new)
    .gather(Gatherers4j.movingSum(3).withOriginal())
    .toList();

// [ 
//   WithOriginal[original=10.0, calculated=13.0]
//   WithOriginal[original=2.0, calculated=14.0]
// ]