iterrows() {
    return enumerate(this);
  }
A generator which returns [row, index location] tuples

pandas equivalent: [DataFrame.iterrows](http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.iterrows.html)

@returns {*}

@example
const df = new DataFrame([{x: 1, y: 2}, {x: 2, y: 3}, {x: 3, y: 4}]);

// Logs 2 4 6
for(const [row, idx] of df) {
  console.log(row.get('x') * 2);
}