updateString = function updateString(idx) {
        var s = ''; // $FlowFixMe TODO
        _this7.columns.forEach(function (k) {
          s += _this7.get(k).iloc(idx) + ',';
        });
        return s;
      }
Convert the `DataFrame` to a csv string

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

@returns {string}

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

// Returns x,y,\r\n1,2,\r\n2,3\r\n3,4\r\n
df.to_csv();