remindToFloss.js

function remindToFloss() {
  var ss = SpreadsheetApp.openById("INSERT SHEET ID HERE");
  var responses = ss.getSheets()[0].getDataRange();
  var participants = ss.getSheets()[1].getDataRange();

  var needsNotifying = [];

  // Compile a list of email addresses that may need notifications
  for (var i = 0; i <= participants.getNumRows() - 1; i++) {
    var email = participants.getValues()[i][0];
    needsNotifying.push(email);
  }
  
  var numRows = responses.getNumRows();
  var values = responses.getValues();

  // Loop through rows in the spreadsheet - starting at the LAST row, since it's likely to be most recent, to speed up the search; only keep searching as long as there are users in the "needs notifying" list
  for (var i = numRows - 1; i >= 1 && needsNotifying.length > 0; i--) {
    var row = values[i];
    var flossDate = row[0];
    var email = row[1];
    var today = new Date();
    var userIndex = needsNotifying.indexOf(email);
    
    // If the user has an entry matching today's date, remove ('pop') them from the list of users to notify today
    if (userIndex >= 0 && today.toDateString() == flossDate.toDateString()) {
      needsNotifying.pop(userIndex);
    }
  }
  
  for (var i in needsNotifying) {
    var email = needsNotifying[i];
    MailApp.sendEmail(email, "Did You Floss Today?", "It looks like you forgot to floss today!\n\nRemember to log your flossing here: https://docs.google.com/a/umn.edu/forms/d/1BtLGon001MVjrD6N8_JTLjYsWF3D3r3ro9bs0z-WOyc/viewform")
  }
};