_checkMissingValue = function _checkMissingValue(v) {
	        return [NaN, null, undefined].includes(v);
	      }
Sort DataFrame rows based on column values. The row should contains only one variable type. Columns are sorted left-to-right.
@param {String | Array<string>} columnNames The columns giving order.
@param {Boolean} [reverse=false] Reverse mode. Reverse the order if true.
@param {String} [missingValuesPosition='first'] Define the position of missing values (undefined, nulls and NaN) in the order.
@returns {DataFrame} An ordered DataFrame.
@example
df.sortBy('id')
df.sortBy(['id1', 'id2'])
df.sortBy(['id1'], true)