Google Spreadsheet to dictionary in Google Apps Script

sheet_to_dict.gs

// dictionary of columns (list)
// thedict = {'<col_header0>': ['<row0>','<row1>',...], '<col_header1>': ['<row0', '<row1>',...]...}
function sheet_to_dict(spreadsheetid, sheetname) {
  var result_dict = {};
  var dataspreadsheet = SpreadsheetApp.openById(spreadsheetid);
  var sheet = dataspreadsheet.getSheetByName(sheetname);
  var cols = sheet.getLastColumn();
  var rows = sheet.getLastRow();

  var data = sheet.getDataRange().getValues();
  // data[row][col]

  for (var c = 0; c < cols; c++) {
    var header = data[0][c];
    var col_data_list = [];
    for(var r = 1; r < rows; r++) {
      var cell_data = data[r][c];
      if(cell_data !== ''){
        col_data_list.push(cell_data);
      }
    }
    if (col_data_list.length > 0) {
      result_dict[data[0][c]] = col_data_list;
    }
  }
  return result_dict;
}