std::vector<std::string> tokens;

std::vector<unsigned int> places;

for (unsigned int index = 0; index < strings.size(); index++) {

if(StringVector::is_na(strings[index])) {

places.push_back(tokens.size());

tokens.push_back("");

continue;

}

std::string str = std::string(strings(index));

typedef boost::tokenizer<boost::char_separator<char> > tokenizer;

boost::char_separator<char> sep(" \f\n\r\t\v");

tokenizer tok(str, sep);

for (tokenizer::iterator it = tok.begin();

it != tok.end();

++it) {

tokens.push_back(*it);

}

}

StringVector y = wrap(tokens);

for(unsigned int i = 0; i < places.size(); i++) {

y[places[i]] = NA_STRING;

}

return y;