Created
March 31, 2014 02:44
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zip in java8
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import java.util.Arrays; | |
import java.util.Iterator; | |
import java.util.List; | |
import java.util.function.BiFunction; | |
import java.util.stream.LongStream; | |
import java.util.stream.Stream; | |
/** | |
* | |
*/ | |
public class StreamUtil { | |
public static <T, U, R> Stream<R> zip(Stream<T> s1, Stream<U> s2, BiFunction<T,U,R> f) { | |
Iterator<U> itr = s2.iterator(); | |
return s1.filter(x-> itr.hasNext()).map(x -> f.apply(x, itr.next())); | |
} | |
public static <T,U> Stream<Pair<T,U>> zip(Stream<T> s1, Stream<U> s2) { | |
return zip(s1, s2, (a, b) -> new Pair(a, b)); | |
} | |
public static <T> Stream<Pair<T,Long>> zipWithIndex(Stream<T> s1) { | |
return zip(s1, LongStream.iterate(0, n -> n +1).boxed()); | |
} | |
public static class Pair<T, U> { | |
final public T _1; | |
final public U _2; | |
public Pair(T t, U u) { | |
_1 = t; | |
_2 = u; | |
} | |
@Override public boolean equals(Object o1){ | |
if (o1 instanceof Pair) { | |
Pair p = (Pair)o1; | |
return _1.equals(p._1) && _2.equals(p._2); | |
} | |
return false; | |
} | |
@Override public int hashCode() { | |
int hash = 1; | |
hash = hash * 31 + _1.hashCode(); | |
hash = hash * 31 + _2.hashCode(); | |
return hash; | |
} | |
@Override public String toString(){ | |
return "(" + _1 + "," + _2 +")"; | |
} | |
} | |
//test | |
public static void main(String[] args) { | |
List<String> list = Arrays.asList("1", "2", "3", "4"); | |
Stream<String> s1 = list.stream(); | |
Stream<String> s2 = list.stream().skip(1); | |
Stream<Pair<String, String>> zip = zip(s1, s2); | |
// lazy evalution | |
zip.map(p -> Integer.parseInt(p._1) *10 + Integer.parseInt(p._2)) | |
.forEach(System.out::println); | |
zipWithIndex(list.stream()).forEach(System.out::println); | |
} | |
} |
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Nice!