I created a Google Sheet to organize short bursts of lesson plan content across grade and content levels at Dever School. Script automatically deletes out-of-date entries. Script will also sort the page after deleting duplicates so that up-to-date information appears first.

removeDuplicates.js

/*
I created a Google Sheet to organize short bursts of lesson plan content across grade and content levels at Dever School.
Script automatically deletes out-of-date entries.
Script will also sort the page after deleting duplicates so that up-to-date information appears first.
*/

function removeDuplicates(){
Logger.clear();
Logger.log("starting over...");
  var ss = SpreadsheetApp.openById(**ID NUMBER HERE **); //get spreadsheet
  var sheet = ss.getSheets()[0]; //specify sheet
  var lastRow = sheet.getLastRow(); //find last row
  var newD = sheet.getRange(1, 1, lastRow, 1).getValues().toString(); //import two copies of 1st to check email against one another
  var oldD = sheet.getRange(1, 1, lastRow, 1).getValues().toString();
  var newData = newD.split(","); //split into arrays
  var oldData = oldD.split(",");
  
  for(i=lastRow; i>0; i--){ //start at bottom of sheet (newest entries, keep this data)
     for(j=0; j<lastRow; j++){ //cross-check from top of sheet (oldest entries, delete this data)
       var jK=j+1; //match array # (starts w/ 0) to row # in spreadsheet (starts w/ 1)
       if(newData[i] == oldData[j] && i!==j){ 
         //if emails match, delete old row and start over
         //this resets the lastRow and for loops to adjust for the deleted data
        Logger.log(oldData[j] + " in row " + jK + " deleted.*************");
        sheet.deleteRow(jK);
        lastRow = sheet.getLastRow();
        newD = sheet.getRange(1, 1, lastRow, 1).getValues().toString();
        oldD = sheet.getRange(1, 1, lastRow, 1).getValues().toString();
        newData = newD.split(",");
        oldData = oldD.split(",");
        i=lastRow;
        j=0;
       } // if
       Logger.log("Old row " + jK + " completed.");
     } // for j
    Logger.log("Done with new row " + i);
  } // for i  
  
  var range = sheet.getRange('A2:C100');
  range.sort({column: 3, ascending: false}); //sort data so that newest is on top
  Logger.log("sheet sorted!");
}