# Change Log Site [llms.txt](/gatherers4j/llms.txt) --- ## v0.15.0 [Released 2026-10-11](https://github.com/tginsberg/gatherers4j/releases/tag/v0.15.0) + Breaking change: the BigDecimal-based moving and running gatherers (sum, product, simple average, exponential average, median, geometric mean, standard deviation) now return `BigDecimalMovingStatGatherer` or `BigDecimalRunningStatGatherer`. The public classes they used to return are removed: `BigDecimalGatherer`, `BigDecimalExponentialMovingAverageGatherer`, `BigDecimalGeometricMeanGatherer`, `BigDecimalMedianGatherer`, `BigDecimalMovingGeometricMeanGatherer`, `BigDecimalMovingProductGatherer`, `BigDecimalMovingSumGatherer`, `BigDecimalProductGatherer`, `BigDecimalSimpleAverageGatherer`, `BigDecimalSimpleMovingAverageGatherer`, `BigDecimalStandardDeviationGatherer`, and `BigDecimalSumGatherer`. Code that only calls the factory methods on `Gatherers4j` is unaffected, but code that names these types (for example in a variable declaration) must change. + Breaking change: remove the public `SamplePercentageGatherers.poisson()`. Use `Gatherers4j.samplePercentage()` instead. + Behavior change: the BigDecimal gatherers now round each input to the `MathContext` as it arrives, and sums, means, and standard deviations then accumulate exactly instead of rounding at every step. Results can differ from v0.14.0 in the final digits. Other numeric changes: + `exponentialMovingAverageWithAlpha()`, `exponentialMovingAverageWithPeriod()`, and their `By` variants now round at every step. Previously they never rounded, so results gained digits with every element and long streams became progressively slower. + Sample standard deviation (`Dataset.Sample`) now emits nothing for the first element, where `runningSampleStandardDeviation()` emitted `0`. + `treatNullAsOne()` and `withMathContext()` are now available on all of the BigDecimal gatherers. + Rename `simpleMovingAverage()`, `simpleMovingAverageBy()`, `simpleRunningAverage()`, and `simpleRunningAverageBy()` to `movingMean()`, `movingMeanBy()`, `runningMean()`, and `runningMeanBy()`. + Replace `runningPopulationStandardDeviation()`, `runningPopulationStandardDeviationBy()`, `runningSampleStandardDeviation()`, and `runningSampleStandardDeviationBy()` with `runningStandardDeviation(Dataset)` and `runningStandardDeviationBy(Dataset, Function)`. + Implement `movingStandardDeviation(Dataset, int)` and `movingStandardDeviationBy(Dataset, int, Function)`. + Fix bug in `sampleFixedSize()` where elements were not sampled with equal probability. The first `sampleSize` elements were chosen too rarely and later elements too often. + Implement `sampleFixedSize(int, RandomGenerator)` and `samplePercentage(double, RandomGenerator)` so callers can specify the source of randomness. + `samplePercentage()` now rejects `NaN`, which was previously accepted and silently emitted nothing. + `exponentialMovingAverageWithAlpha()` and `exponentialMovingAverageWithAlphaBy()` now reject `NaN` when called, instead of failing with `NumberFormatException` when the stream runs. + `withMathContext()` on the BigDecimal gatherers now rejects a `MathContext` with a precision of 0, such as `MathContext.UNLIMITED`, which made most statistics throw `ArithmeticException` when the stream ran. + Implement `movingHarmonicMean()`, `movingHarmonicMeanBy()`, `runningHarmonicMean()`, and `runningHarmonicMeanBy()`. + Implement `movingRootMeanSquare()`, `movingRootMeanSquareBy()`, `runningRootMeanSquare()`, and `runningRootMeanSquareBy()`. + Implement `movingVariance()`, `movingVarianceBy()`, `runningVariance()`, and `runningVarianceBy()` + Implement `movingStatistics()`, `movingStatisticsBy()`, `runningStatistics()`, and `runningStatisticsBy()`, which emit a `StatisticalSummary` record (count, sum, mean, min, max, and population and sample variance and standard deviation) for each element. + Implement `movingPercentile()`, `movingPercentileBy()`, `runningPercentile()`, and `runningPercentileBy()`. + Implement `movingWeightedMean()` and `movingWeightedMeanBy()`, the weighted moving average. Weights run linearly from 1 (oldest) to the window size (newest) by default, or can be supplied as a `List` (or `BigDecimal...` for `movingWeightedMean()`) ordered oldest to newest. + Fix `movingProduct()`, `movingProductBy()`, `movingGeometricMean()`, and `movingGeometricMeanBy()` accumulating rounding error over long streams. Values leaving the window are no longer divided out of the product, and each step still takes constant time. + Fix `movingMin()`, `movingMinBy()`, `movingMax()`, and `movingMaxBy()` slowing down in proportion to the window size on steadily rising or falling input, and evicting the wrong values after about 2.1 billion elements. + Fix `movingGeometricMean()`, `runningGeometricMean()`, and their `By` variants throwing `NumberFormatException` or returning wrong results when the product of the values is outside the range of a `double` (above about 1E+308 or below about 1E-308). ## v0.14.0 [Released 2026-05-17](https://github.com/tginsberg/gatherers4j/releases/tag/v0.14.0) + Implement `movingGeometricMean()`, `movingGeometricMeanBy()`, `runningGeometricMean()`, and `runningGeometricMeanBy()`. + Implement `filterNotNull()`, which filters out null values from the input stream and is useful for lining up JSpecify annotations (from nullable to non-nullable). + Fix bug in `movingProduct()` and `movingProductBy()` where zero values were incorrectly handled. Addresses [#184](https://github.com/tginsberg/gatherers4j/issues/184). + Change `CrossGatherer`, `TypeFilteringGatherer`, and `FlattenSingleOrFail` to use Greedy integrators. + Thank you to [@Riggs333](https://github.com/Riggs333) for contributing code cleanups, making comparisons in `FrequencyGatherer` easier to understand! + Thank you to [@Riggs333](https://github.com/Riggs333) for contributing changes to tests to use AssertJ's type-specific exception assertions, which clarifies the intent of the code! ## v0.13.0 [Released 2026-01-04](https://github.com/tginsberg/gatherers4j/releases/tag/v0.13.0) + Behavior change: All "moving" gatherers will now include all calculated values by default, even when the full lookback window has not been reached. + To turn this behavior off, use `excludePartialValues()`. + Previously, partial results were suppressed and turned on via `includePartialValues()`. + This affects `movingMax()`, `movingMaxBy()`, `movingMin()`, `movingMinBy()`, `movingMedian()`, `movingMedianBy()`, `movingProduct()`, `movingProductBy()`, `movingSum()`, `movingSumBy()`, `simpleMovingAverage()`, and `simpleMovingAverageBy()` + Implement `uniquelyOccurringBy()` to limit the stream to uniquely occurring elements as measured by the given function + Implement `movingMedian()` and `movingMedianBy()` + Implement `runningMedian()` and `runningMedianBy()` + Implement `movingMax()`, `movingMaxBy()`, `movingMin()`, and `movingMinBy()` + Implement `runningMax()`, `runningMaxBy()`, `runningMin()`, and `runningMinBy()` + Fixes to documentation ## v0.12.0 [Released 2025-09-27](https://github.com/tginsberg/gatherers4j/releases/tag/v0.12.0) + Move Java version to 25 (was 24) Addresses [#164](https://github.com/tginsberg/gatherers4j/issues/164) + Support Java Modularization. Addresses [#156](https://github.com/tginsberg/gatherers4j/issues/156), thanks [@Goldmensch](https://github.com/Goldmensch)! + Support parallelization in `UniquelyOccurringGatherer` ## v0.11.0 [Released 2025-05-05](https://github.com/tginsberg/gatherers4j/releases/tag/v0.11.0) + Fix and document behavior of `window()` when there are multiple partial groupings at the end. Addresses [#135](https://github.com/tginsberg/gatherers4j/issues/135), thanks [@paulk-asert](https://github.com/paulk-asert)! + Implement exponential moving averages with `exponentialMovingAverageWithAlpha()`, `exponentialMovingAverageWithAlphaBy()`,`exponentialMovingAverageWithPeriod()`, and `exponentialMovingAverageWithPeriodBy()`. + Change index to be an `int` rather than a `long` in `filterIndexed()`, `foldIndexed()`, `mapIndexed()`, `peekIndexed()`, `scanIndexed()` and `withIndex()`. Addresses [#140](https://github.com/tginsberg/gatherers4j/issues/140). + Optimize `rotate(Left)` to store a minimal set of elements instead of the entire stream. Addresses [#141](https://github.com/tginsberg/gatherers4j/issues/141), thanks [@paulk-asert](https://github.com/paulk-asert)! ## v0.10.0 [Released 2025-03-19](https://github.com/tginsberg/gatherers4j/releases/tag/v0.10.0) + Upgrade the minimum Java version from 23 to 24 + Implement `mapIndexed()` to perform a mapping operation given the element being mapped and its zero-based index + Implement `peekIndexed()` to peek at each element and its zero-based index + Implement `sampleFixedSize()` to randomly sample a fixed number of elements from a stream + Implement `samplePercentage()` to randomly sample a percentage of the stream elements + Rename `IndexedValue` to `WithIndex`, for consistency (matching `WithCount` and `WithOriginal`) ## v0.9.0 [Released 2025-02-23](https://github.com/tginsberg/gatherers4j/releases/tag/v0.9.0) + Implement `filterInstanceOf()` to filter a stream by type more easily. Addresses [#86](https://github.com/tginsberg/gatherers4j/issues/86), thanks [@nipafx](https://github.com/nipafx). + Implement `groupOrdered()`, and `groupOrderedBy()` to appropriately group elements in the input stream to lists in the output stream. Addresses [#88](https://github.com/tginsberg/gatherers4j/issues/88), thanks [@nipafx](https://github.com/nipafx). + Implement `ensureOrdered()` and `ensureOrderedBy()` to ensure the given stream meets an ordering criteria, or fail exceptionally otherwise + Implement `filterOrdered()` and `filterOrderedBy()` to remove non-ordered elements from the input stream + Implement `window()` to provide more options to windowing functions, namely - ability to specify size, how many to skip each time, and whether to include partial windows + Implement `repeat(n)` and `repeatInfinitely()` to repeatedly emit the input stream to the output stream + Implement `rotate(n)` rotate the stream either left or right (consumes entire stream) + Renamed `everyNth(n)` to `takeEveryNth(n)` and added `dropEveryNth(n)` for completeness + Renamed `filterWithIndex()` to `filterIndexed()` to match other indexing Gatherers + Renamed `cross()` to `crossWith()` for consistency + Renamed `interleave()` to `interleaveWith()` for consistency + Renamed `grouping()` to `group()` and `groupingBy()` to `groupBy()` for consistency + Renamed `last()` to `takeLast()` to match `dropLast()` ## v0.8.0 [Released 2025-02-01](https://github.com/tginsberg/gatherers4j/releases/tag/v0.8.0) + Add support for `orElse()` and `orElseEmpty()` on size-based gatherers to provide a non-exceptional output stream + Implement `everyNth()` to get every nth element from the stream + Implement `uniquelyOccurring()` to emit stream elements that occur a single time + Implement `takeUntil()` to take from a stream until a predicate is met, including the first element that matches the predicate + Implement `foldIndexed()` to perform a fold along with the index of each element + Implement `scanIndexed()` to perform a scan along with the index of each element + Implement `intersperse()` to put the given element between each element of the stream + Implement `cross(iterable)`, `cross(iterator)`, and `cross(stream)` to combine elements in the input stream with the given source of elements ## v0.7.0 [Released 2025-01-06](https://github.com/tginsberg/gatherers4j/releases/tag/v0.7.0) + Use greedy integrators where possible (Addresses [#57](https://github.com/tginsberg/gatherers4j/issues/57)) + Add [JSpecify](https://jspecify.dev/) annotations for static analysis + Implement `orderByFrequencyAscending()` and `orderByFrequencyDescending()` + Implement `movingProduct()` and `movingProductBy()` + Implement `movingSum()` and `movingSumBy()` + Remove `maxBy(fn)` and `minBy(fn)`, can be done with JDK methods trivially + Rename `exactSize()` to `sizeExactly()` + Implement `sizeLessThan()`, `sizeLessThanOrEqualTo()`, `sizeGreaterThan()`, and `sizeGreaterThanOrEqualTo()` + API Style - Functions, when used as arguments, should come last for consistency and to play nice with Kotlin (Addresses [#64](https://github.com/tginsberg/gatherers4j/issues/64)) ## v0.6.0 [Released 2024-11-02](https://github.com/tginsberg/gatherers4j/releases/tag/v0.6.0) + Implement `dropLast(n)` + Implement `grouping()` and `groupingBy(fn)` + Add support for `zipWith(iterable)` and `zipWith(iterator)` + With support for: + `argumentWhenSourceLonger(fn)` + `sourceWhenArgumentLonger(fn)` + `nullArgumentWhenSourceLonger()` + `nullSourceWhenArgumentLonger()` + Add support for `interleave(iterable)` and `interleave(iterator)` + With support for: + `appendLonger()` + `appendArgumentIfLonger()` + `appendSourceIfLonger()` ## v0.5.0 [Released 2024-10-13](https://github.com/tginsberg/gatherers4j/releases/tag/v0.5.0) + Implement `reverse()` - Cause a stream to be emitted in reverse (stores entire stream in memory) + Implement `maxBy(fn)` and `minBy(fn)` - Finds the single maximum or minimum value in a stream as defined by the `function` given (stores entire stream in memory) + Implement `exactSize(n)` - Ensures a stream is precisely `n` elements long or throws an `IllegalStateException` (stores entire stream in memory) ## v0.4.0 [Released 2024-10-08](https://github.com/tginsberg/gatherers4j/releases/tag/v0.4.0) + Implement `shuffle()` and `shuffle(RandomGenerator)` + Implement `filterWithIndex()` + Implement `runningProduct()` and `runningProductBy()` + Implement `runningSum()` and `runningSumBy()` + Remove `concat()` implementation (the JDK has this) + Remove `withIndexStartingAt()` from `filterWithIndex()`, not sure if this is a real use case. ## v0.3.0 [Released 2024-10-19](https://github.com/tginsberg/gatherers4j/releases/tag/v0.3.0) + Upgrade the minimum Java version from 22 to 23 ## v0.2.0 [Released 2024-08-22](https://github.com/tginsberg/gatherers4j/releases/tag/v0.2.0) + Added `throttle()` over a time period + Added `debounce()` over a time period ## v0.1.0 [Released 2024-08-13](https://github.com/tginsberg/gatherers4j/releases/tag/v0.1.0) + Added Standard Deviation (population and sample) + Refactored all BigDecimal-based Gatherers + Added concat ## v0.0.1 [Released 2024-07-29](https://github.com/tginsberg/gatherers4j/releases/tag/v0.0.1) + Initial release