nl_tokens: Create a new primitive vector using a subset of the data .
pl_tokens: public PrimitiveVector subset ( int start , int stop , int stride ) { BooleanPrimitiveVector n = new BooleanPrimitiveVector ( getTemplate ( ) ) ; stride = Math . <mask> ( stride , 1 ) ; stop = Math . max ( start , stop ) ; int length = 1 + ( stop - start ) / stride ; n . setLength ( length ) ; int count = 0 ; for ( int i = start ; i <= stop ; i += stride ) { n . setValue ( count , vals [ i ] ) ; count ++ ; } return n ; }