function onOpen() {
  var spreadsheet = SpreadsheetApp.getActive();
  var menuItems = [
    {name: 'Filter duplicate temperatures', functionName: 'filterTemperatures'}
  ];
  spreadsheet.addMenu('Filter', menuItems);
}

function filterTemperatures() {
  var ss = SpreadsheetApp.getActiveSpreadsheet();
  var sheet = ss.getActiveSheet();
  var data = sheet.getDataRange().getValues();
  var filtered = {};
  for (var i = 0; i < 100; i++) {
    var date = data[i][2];
    var minutes = date.substr(-2, 2);
    if (minutes % 5 === 0) {
      var date_hash = Utilities.base64Encode(date);
      var temperature = data[i][1];
      if (!filtered[date_hash]){
        filtered[date_hash] = {temperature: temperature, date: date};
      }
    }
  }

  insertResult(filtered);
}

function insertResult(result) {
  var new_sheet = SpreadsheetApp.getActiveSpreadsheet().insertSheet();
  new_sheet.setName('Result');
  for (var date_hash in result) {
    var row = result[date_hash];
    new_sheet.appendRow([row.temperature, row.date]);
  }
}