sampleFixedSize()

Implementation Notes

This uses the reservoir method internally and guarantees that for streams that are at least sampleSize in length, there will be exactly sampleSize elements in the output stream. Elements will be emitted in the order in which they are encountered. This implementation reads the entire stream before emitting any results, making it inappropriate for infinite streams.

There are two versions of this Gatherer, one that uses the platform default RandomGenerator and one that allows the caller to specify a RandomGenerator. Specifying a RandomGenerator with a fixed seed makes the sample repeatable, which is useful for testing. Most RandomGenerator implementations are not thread-safe, so a single instance of this Gatherer should not be used from multiple threads at the same time.

Signatures

1. sampleFixedSize(int sampleSize)
2. sampleFixedSize(int sampleSize, RandomGenerator randomGenerator)

• sampleSize - A positive number of elements to sample from the stream, randomly
• randomGenerator - (Optional) A RandomGenerator to use as the source of randomness.

Examples

Get a fixed number of elements from the stream, specifying the source of randomness

Stream
    .of("A", "B", "C", "D", "E")
    .gather(Gatherers4j.sampleFixedSize(2, new Random(123)))
    .toList();

// ["A", "E"] 

Get a fixed number of elements from the stream, randomly

Stream
    .of("A", "B", "C", "D", "E")
    .gather(Gatherers4j.sampleFixedSize(2))
    .toList();

// Possibly: ["A", "D"]
// Answer will be different every time