A library of useful Stream Gatherers (custom intermediate operations) for Java 22+.
To use this library, add it as a dependency to your build. This library has no additional dependencies.
Maven
Add the following dependency to pom.xml.
<dependency>
<groupId>com.ginsberg</groupId>
<artifactId>gatherers4j</artifactId>
<version>0.1.0</version>
</dependency>Gradle
Add the following dependency to build.gradle or build.gradle.kts
implementation("com.ginsberg:gatherers4j:0.1.0")| Function | Purpose |
|---|---|
concat(stream) |
Creates a stream which is the concatenation of the source stream and the given stream, which must be of the same type |
dedupeConsecutive() |
Remove consecutive duplicates from a stream |
dedupeConsecutiveBy(fn) |
Remove consecutive duplicates from a stream as returned by fn |
distinctBy(fn) |
Emit only distinct elements from the stream, as measured by fn |
interleave(stream) |
Creates a stream of alternating objects from the input stream and the argument stream |
last(n) |
Constrain the stream to the last n values |
withIndex() |
Maps all elements of the stream as-is along with their 0-based index |
withIndexStartingAt(n) |
Maps all elements of the stream as-is along with an index starting at the number specified |
zipWith(stream) |
Creates a stream of Pair objects whose values come from the input stream and argument stream |
zipWithNext() |
Creates a stream of List objects via a sliding window of width 2 and stepping 1 |
| Function | Purpose |
|---|---|
runningPopulationStandardDeviation() |
Create a stream of BigDecimal objects representing the running population standard deviation. |
runningPopulationStandardDeviationBy(fn) |
Create a stream of BigDecimal objects as mapped from the input via fn, representing the running population standard deviation. |
runningSampleStandardDeviation() |
Create a stream of BigDecimal objects representing the running sample standard deviation. |
runningSampleStandardDeviationBy(fn) |
Create a stream of BigDecimal objects as mapped from the input via fn, representing the running sample standard deviation. |
simpleMovingAverage(window) |
Create a moving average of BigDecimal values over the previous window values. See below for options. |
simpleMovingAverageBy(fn, window) |
Create a moving average of BigDecimal values over the previous window values, as mapped via fn. |
simpleRunningAverage() |
Create a running average of BigDecimal values. See below for options. |
simpleRunningAverageBy(fn) |
Create a running average of BigDecimal values as mapped via fn. |
Stream
.of("1.0", "2.0", "10.0")
.map(BigDecimal::new)
.gather(Gatherers4j.simpleRunningAverage())
.toList();
// [1, 1.5, 4.3333333333333333]Stream
.of("1.0", "2.0", "10.0", "20.0", "30.0")
.map(BigDecimal::new)
.gather(Gatherers4j.simpleMovingAverage(2))
.toList();
// [1.5, 6, 15, 25]Stream
.of("A", "B", "C")
.gather(Gatherers4j.concat(Stream.of("D", "E", "F")))
.toList();
// ["A", "B", "C", "D", "E", "F"]Stream
.of("A", "B", "C")
.gather(Gatherers4j
.concat(Stream.of("D", "E", "F"))
.concat(Stream.of("G", "H", "I")) // concat can be called again for more streams
)
.toList();
// ["A", "B", "C", "D", "E", "F", "G", "H", "I"]Stream
.of("A", "A", "A", "B", "B", "C", "C", "D", "A", "B", "C")
.gather(Gatherers4j.dedupeConsecutive())
.toList();
// ["A", "B", "C", "D", "A", "B", "C"]record Person(String firstName, String lastName) {}
Stream
.of(
new Person("Todd", "Ginsberg"),
new Person("Emma", "Ginsberg"),
new Person("Todd", "Smith")
)
.gather(Gatherers4j.dedupeConsecutiveBy(Person::lastName))
.toList();
// [Person("Todd", "Ginsberg"), Person("Todd", "Smith")]record Person(String firstName, String lastName) {}
Stream
.of(
new Person("Todd", "Ginsberg"),
new Person("Emma", "Ginsberg"),
new Person("Todd", "Smith")
)
.gather(Gatherers4j.distinctBy(Person::firstName))
.toList();
// [Person("Todd", "Ginsberg"), Person("Emma", "Ginsberg")]final Stream<String> left = Stream.of("A", "B", "C");
final Stream<String> right = Stream.of("D", "E", "F");
left.gather(Gatherers4j.interleave(right)).toList();
// ["A", "D", "B", "E", "C", "F"]Stream
.of("A", "B", "C", "D", "E", "F", "G")
.gather(Gatherers4j.last(3))
.toList();
// ["E", "F", "G"]Stream
.of("A", "B", "C")
.gather(Gatherers4j.withIndex())
.toList();
// [IndexedValue(0, "A"), IndexedValue(1, "B"), IndexedValue(2, "C")]The left and right streams can be of different types.
final Stream<String> left = Stream.of("A", "B", "C");
final Stream<Integer> right = Stream.of(1, 2, 3);
left.gather(Gatherers4j.zip(right)).toList();
// [Pair("A", 1), Pair("B", 2), Pair("C", 3)] This converts a Stream<T> to a Stream<List<T>>
Stream
.of("A", "B", "C", "D", "E")
.gather(Gatherers4j.zipWitNext())
.toList();
// [["A", "B"], ["B", "C"], ["C", "D"], ["D", "E"]]Functions which modify output and are available on all BigDecimal gatherers (simple average, moving average, and standard deviation).
| Function | Purpose |
|---|---|
treatNullAsZero() |
When an element in the Stream<BigDecimal> is null treat it as BigDecimal.ZERO instead of skipping it in the calculation. |
treatNullAs(BigDecimal) |
When an element in the Stream<BigDecimal> is null treat it as the BigDecimal value given instead of skipping it in the calculation. |
withMathContext(MathContext) |
Switch the MathContext for all calculations to the non-null MathContext given. The default is MathContext.DECIMAL64. |
withOriginal() |
Include the original stream value in addition to the calculated value. |
Note that rounding mode, precision, and scale are derived from the MathContext.
This example creates a stream of double, converts each value to a BigDecmial, and takes a simpleMovingAverage over 10 trailing values.
It will includePartialValues and sets the MathContext to the values given. Additionally, nulls
are treated as zeros, and the calculated average is returned along with the original value.
someStreamOfBigDecimal()
.gather(Gatherers4j
.averageBigDecimals()
.simpleMovingAverage(10)
.includePartialValues()
.withMathContext(MathContext.DECIMAL32)
.treatNullAsZero()
.withOriginal()
)
.toList();
// Example output:
[
WithOriginal[original=0.8462487, calculated=0.8462487],
WithOriginal[original=0.8923297, calculated=0.8692890],
WithOriginal[original=0.2556937, calculated=0.6647573],
WithOriginal[original=0.2901778, calculated=0.5711125],
WithOriginal[original=0.4945578, calculated=0.5558016],
WithOriginal[original=0.3173066, calculated=0.5160525],
WithOriginal[original=0.6377766, calculated=0.5334417],
WithOriginal[original=0.1729199, calculated=0.4883765],
WithOriginal[original=0.7408201, calculated=0.5164258],
WithOriginal[original=0.7169926, calculated=0.5364825],
WithOriginal[original=0.5174489, calculated=0.5036025],
WithOriginal[original=0.5895662, calculated=0.4733262],
WithOriginal[original=0.4458275, calculated=0.4923396],
// etc...
]- Consider adding a gatherer if it cannot be implemented with
map,filter, or a collector without enclosing outside state. - Resist the temptation to add functions that only exist to provide an alias. They seem fun/handy but add surface area to the API and must be maintained forever.
- All features should be documented and tested.
Please feel free to file issues for change requests or bugs. If you would like to contribute new functionality, please contact me before starting work!
Copyright © 2024 by Todd Ginsberg