public Iterable < Integer > index ( ) { return ( ) -> new Iterator < Integer > ( ) { private final Iterator < Integer > it = data . records . keySet ( ) . iterator ( ) ; /** {@inheritDoc} */ @ Override public boolean hasNext ( ) { return it . hasNext ( ) ; } /** {@inheritDoc} */ @ Override public Integer next ( ) { return it . next ( ) ; } /** {@inheritDoc} */ @ Override public void remove ( ) { throw new UnsupportedOperationException ( "This is a read-only iterator, remove operation is not supported." ) ; } } ; }
Returns a read - only Iterable on the keys of the Dataframe .