code: function areColumnsEqualLength(columns) {
    if (columns.length <= 1) {
      return true;
    }
    var firstLength = columns[0].values.length;
    var columnsWithTheSameLength = columns.slice(1).filter(function(column) {
      return column.values.length === firstLength;
    });
    return columnsWithTheSameLength.length === columns.length - 1;
  }
docs: Normally a TableStructure is generated from a csvString, using loadFromCsv, or via loadFromJson.
  However, if its columns are set directly, we should check the columns are all the same length.
  @private
  @param  {Concept[]} columns Array of columns to check.
  @return {Boolean} True if the columns are all the same length, false otherwise.