Is there a concise way to iterate over a stream with indices in Java 8?
java, java-8, java-stream
Solution
The cleanest way is to start from a stream of indices:
String[] names = {"Sam", "Pamela", "Dave", "Pascal", "Erik"};
IntStream.range(0, names.length)
.filter(i -> names[i].length() <= i)
.mapToObj(i -> names[i])
.collect(Collectors.toList());
The resulting list contains "Erik" only.
One alternative which looks more familiar when you are used to for loops would be to maintain an ad hoc counter using a mutable object, for example an `AtomicInteger`:
String[] names = {"Sam", "Pamela", "Dave", "Pascal", "Erik"};
AtomicInteger index = new AtomicInteger();
List<String> list = Arrays.stream(names)
.filter(n -> n.length() <= index.incrementAndGet())
.collect(Collectors.toList());
Note that using the latter method on a parallel stream could break as the items would not necesarily be processed "in order".
Problem
Is there a concise way to iterate over a stream whilst having access to the index in the stream? ``` String[] names = {"Sam","Pamela", "Dave", "Pascal", "Erik"}; List<String> nameList; Stream<Integer> indices = intRange(1, names.length).boxed(); nameList = zip(indices, stream(names), SimpleEntry::new) .filter(e -> e.getValue().length() <= e.getKey()) .map(Entry::getValue) .collect(toList()); ``` which seems rather disappointing compared to the LINQ example given there ``` string[] names = { "Sam", "Pamela", "Dave", "Pascal", "Erik" }; var nameList = names.Where((c, index) => c.Length <= index + 1).ToList(); ``` Is there a more concise way? Further it seems the zip has either moved or been removed...