add slice with unit tests

src/main/java/de/downgra/jitertools/JIterTools.java

@@ -619,4 +619,69 @@ public static <T> Iterable<T> ncycles(final Iterable<T> iterable,
 			final int n) {
 		return chain(repeat(iterable, n));
 	}
+
+	public static <T> Iterable<T> slice(final Iterable<T> iterable,
+			final int stop) {
+		return slice(iterable, 0, stop, 1);
+	}
+
+	public static <T> Iterable<T> slice(final Iterable<T> iterable,
+			final int start, final int stop) {
+		return slice(iterable, start, stop, 1);
+	}
+
+	public static <T> Iterable<T> slice(final Iterable<T> iterable,
+			final int start, final int stop, final int step) {
+		assert step > 0;
+		assert start <= stop;
+		return new Iterable<T>() {
+			@Override
+			public Iterator<T> iterator() {
+				return new Iterator<T>() {
+					final Iterator<Integer> _counter = range(start, stop < 0 ? Integer.MAX_VALUE : stop, step)
+							.iterator();
+					final Iterator<Pair<Integer, T>> _iterator = enumerate(
+							iterable).iterator();
+					Integer _current_counter = _counter.hasNext() ? _counter
+							.next() : null;
+					T _last = null;
+
+					private final void consume() {
+						if (_last == null) {
+							while (_iterator.hasNext()
+									&& _current_counter != null) {
+								Pair<Integer, T> p = _iterator.next();
+								if (p.getFirst() == _current_counter) {
+									_last = p.getSecond();
+									if (_counter.hasNext()) {
+										_current_counter = _counter.next();
+									}
+									return;
+								}
+							}
+						}
+					}
+
+					@Override
+					public boolean hasNext() {
+						consume();
+						return _last != null;
+					}
+
+					@Override
+					public T next() {
+						consume();
+						T ret = _last;
+						_last = null;
+						return ret;
+					}
+
+					@Override
+					public void remove() {
+					}
+				};
+			}
+		};
+	}
+
 }

src/test/java/de/downgra/jitertools/TestSlice.java

@@ -0,0 +1,48 @@
+package de.downgra.jitertools;
+
+import static de.downgra.jitertools.JIterTools.list;
+import static de.downgra.jitertools.JIterTools.range;
+import static de.downgra.jitertools.JIterTools.slice;
+import static org.junit.Assert.assertArrayEquals;
+
+import java.util.ArrayList;
+
+import org.junit.Test;
+
+public class TestSlice {
+
+	@Test
+	public void stop() {
+		assertArrayEquals(new Integer[] { 0, 1, 2, 3, 4 }, list(
+				slice(range(10), 5)).toArray());
+		assertArrayEquals(new Integer[] {}, list(slice(range(10), 0)).toArray());
+		assertArrayEquals(new Integer[] { 3, 4, 5 },
+				list(slice(range(3, 6), 3)).toArray());
+	}
+
+	@Test
+	public void startStop() {
+		assertArrayEquals(new Integer[] { 2, 3, 4 }, list(
+				slice(range(10), 2, 5)).toArray());
+		assertArrayEquals(new Integer[] {}, list(slice(range(10), 0, 0))
+				.toArray());
+	}
+
+	@Test
+	public void startStopStep() {
+		assertArrayEquals(new Integer[] { 2, 4, 6 }, list(
+				slice(range(10), 2, 8, 2)).toArray());
+	}
+
+	@Test
+	public void empty() {
+		assertArrayEquals(new Integer[] {}, list(
+				slice(new ArrayList<Integer>(), 2)).toArray());
+	}
+
+	@Test
+	public void noStop() {
+		assertArrayEquals(new Integer[] { 0, 33, 66, 99 }, list(
+				slice(range(100), 0, -1, 33)).toArray());
+	}
+}