org.roaringbitmap

Interface PeekableIntIterator

All Superinterfaces:

Cloneable, IntIterator

All Known Implementing Classes:

BufferIntIteratorFlyweight, IntIteratorFlyweight

public interface PeekableIntIterator
extends IntIterator

Simple extension to the IntIterator interface. It allows you to "skip" values using the advanceIfNeeded method, and to look at the value without advancing (peekNext). This richer interface enables efficient algorithms over iterators of integers.

Method Summary

Modifier and Type	Method and Description
void	advanceIfNeeded(int minval) If needed, advance as long as the next value is smaller than minval The advanceIfNeeded method is used for performance reasons, to skip over unnecessary repeated calls to next.
PeekableIntIterator	clone() Creates a copy of the iterator.
int	peekNext() Look at the next value without advancing The peek is useful when working with several iterators at once.

Methods inherited from interface org.roaringbitmap.IntIterator

hasNext, next

Method Detail

advanceIfNeeded

void advanceIfNeeded(int minval)

If needed, advance as long as the next value is smaller than minval The advanceIfNeeded method is used for performance reasons, to skip over unnecessary repeated calls to next. Suppose for example that you wish to compute the intersection between an ordered list of integers (e.g., int[] x = {1,4,5}) and a PeekableIntIterator. You might do it as follows...

     PeekableIntIterator j = // get an iterator
     int val = // first value from my other data structure
     j.advanceIfNeeded(val);
     while ( j.hasNext() ) {
       if(j.next() == val) {
         // ah! ah! val is in the intersection...
         // do something here
         val = // get next value?
       }
       j.advanceIfNeeded(val);
     }
     

The benefit of calling advanceIfNeeded is that each such call can be much faster than repeated calls to "next". The underlying implementation can "skip" over some data.

Parameters:

minval - threshold

peekNext

int peekNext()

Look at the next value without advancing The peek is useful when working with several iterators at once. Suppose that you have 100 iterators, and you want to compute their intersections without materializing the result. You might do it as follows...

    PriorityQueue pq = new PriorityQueue(100,
      new Comparator<PeekableIntIterator>() {
             public int compare(PeekableIntIterator a,
                                PeekableIntIterator b) {
                 return a.peek() - b.peek();
             }
         });
 
    //...  populate pq
    
    while(! pq.isEmpty() ) {
      // get iterator with a smallest value
      PeekableIntIterator pi = pq.poll();
      int x = pi.next(); // advance
      // do something with x
      if(pi.hasNext()) pq.add(pi)
    }
    

Notice how the peek method allows you to compare iterators in a way that the next method could not do.

Returns:

next value

clone

PeekableIntIterator clone()

Creates a copy of the iterator.

Specified by:

clone in interface IntIterator

Returns:

a clone of the current iterator