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@smac89
Last active May 10, 2020 05:53
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Java sliding windows via Streams
import java.util.List;
import java.util.stream.IntStream;
import java.util.stream.Stream;
public class Main {
public static void main(String args[]) {
Stream<List<Integer>> stream = SlidingWindow.pagedStream(StreamableSupplier.fromStream(IntStream.range(1, 10000).boxed()), 5)
.apply(i -> i <= 100);
stream.forEach(System.out::println);
}
}
import java.util.ArrayList;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Spliterators;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;
public class SlidingWindow {
public static <T> Function<Predicate<? super T>, Stream<List<T>>> pagedStream(StreamableSupplier<T> supplier, final int pageSize) {
return pagedStream(supplier, pageSize, 1);
}
public static <T> Function<Predicate<? super T>, Stream<List<T>>> pagedStream(StreamableSupplier<T> supplier,
final int pageSize,
int slideAmount) {
return pagedStream(supplier, pageSize, slideAmount, 0);
}
public static <T> Function<Predicate<? super T>, Stream<List<T>>> pagedStream(StreamableSupplier<T> supplier,
final int pageSize,
final int slideAmount,
int offset) {
return (stopPredicate) -> StreamSupport.stream(Spliterators.spliteratorUnknownSize(new Iterator<List<T>>() {
LinkedList<T> window = new LinkedList<>();
boolean hasFinished = false;
{
assert pageSize > 0;
assert slideAmount > 0;
for (int i = 0; i < offset; i++) {
T temp = supplier.get();
if (!stopPredicate.test(temp)) {
hasFinished = true;
break;
}
}
}
@Override
public boolean hasNext() {
return !hasFinished;
}
@Override
public List<T> next() {
if (hasFinished) {
throw new NoSuchElementException("The iterator is empty!");
}
hasFinished = populate();
List<T> currWindow = new ArrayList<>(window);
if (!hasFinished) {
hasFinished = slide();
}
return currWindow;
}
private boolean populate() {
boolean added = false;
while (window.size() < pageSize) {
T item = supplier.get();
if (!stopPredicate.test(item)) {
break;
}
window.add(item);
added = true;
}
if (added) {
return window.size() != pageSize;
}
window.clear();
return false;
}
private boolean slide() {
for (int p = 0; p < slideAmount; p++) {
if (!window.isEmpty()) {
window.pop();
} else if (!stopPredicate.test(supplier.get())) {
return true;
}
}
return false;
}
}, 0), false);
}
}
import java.util.Iterator;
import java.util.Spliterators;
import java.util.function.Supplier;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;
@FunctionalInterface
public interface StreamableSupplier<T> {
T get();
static <T> StreamableSupplier<T> fromStream(Stream<T> stream) {
Iterator<T> streamIterator = stream.iterator();
return streamIterator::next;
}
static <T> StreamableSupplier<T> fromSupplier(Supplier<T> supplier) {
return supplier::get;
}
default Stream<T> toStream() {
return StreamSupport.stream(Spliterators.spliteratorUnknownSize(new Iterator<T>() {
@Override
public boolean hasNext() {
return true;
}
@Override
public T next() {
return get();
}
}, 0), false);
}
}
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