Overwriting Google sheets (for form response) rows if duplicate entered - google-apps-script

Question

So, I've been trying to figure out how to stop the duplicate rows appearing in my google sheets response output from a google form. If found this link which sounds like it does exactly what I want (Form Google Script Prevent Duplicates), but cannot for the life of me work out how to edit the given answer to work on my sheet.
I have included a screenshot of my workbook to give an example of the structure of the data I'd like the edited code to run on, and also below is my attempt at making the code run correctly on my data structure.
My sheet structure that I'd like to run the code on. I want to use the email address as the 'unique' identifier, so any duplicate rows can be identified using that.
My attempt at adapting the code to work on the above data structure (I have absolutely no background with this scripting language, so please go easy on me if I've made a glaringly obvious error):
function updateExisting() {
var s = SpreadsheetApp.getActiveSheet(),
// s = ss.getSheetByName(''),
lastRow = s.getLastRow(),
lastValues = s.getRange('A'+lastRow+':C'+lastRow).getValues(),
name = lastValues[0][0],
allNames = s.getRange('B2:B').getValues(),
row, len;
// TRY AND FIND EXISTING NAME
for (row = 0, len = allNames.length; row < len - 1; row++)
if (allNames[row][0] == name) {
// OVERWRITE OLD DATA
s.getRange('A2').offset(0, 0, row,
lastValues.length).setValues([lastValues]);
// DELETE THE LAST ROW
s.deleteRow(lastRow);
break;}
}

Answer 1

Key words: duplicates, Google, spreadsheet, Sheets, Form, submission, edit, row, unique.
This code prevents duplicates in a Google Sheet when submitting a Google Form, by overwriting an existing row with the existing unique value, if one exists.
The code searches one column in a spreadsheet and looks for a match. I tried to make it generic so that the code doesn't need to be changed depending upon what column the unique identifier is in. You need to make a couple of settings in the "User Settings" section to make it work. But that is better than needing to rewrite the code.
function updateExisting(columnWithUniqueIdentifier,sheetTabName) {
var dataFromColumnToMatch,lastColumn,lastRow,rowWithExistingUniqueValue,rowOfDataJustSaved,
sh,ss,valueToSearchFor;
// USER SETTINGS - if the values where not passed in to the function
if (!columnWithUniqueIdentifier) {//If you are not passing in the column number
columnWithUniqueIdentifier = 2;//Hard code column number if you want
}
if (!sheetTabName) {//The sheet tab name was not passed in to the function
sheetTabName = "Put your Sheet tab name here";//Hard code if needed
}
//end of user settings
ss = SpreadsheetApp.getActiveSpreadsheet();//Get the active spreadsheet - this code must be in a project bound to spreadsheet
sh = ss.getSheetByName(sheetTabName);
lastRow = sh.getLastRow();
lastColumn = sh.getLastColumn();
//Logger.log('lastRow: ' + lastRow)
rowOfDataJustSaved = sh.getRange(lastRow, 1, 1, lastColumn).getValues();//Get the values that were just saved
valueToSearchFor = rowOfDataJustSaved[0][columnWithUniqueIdentifier-1];
//Logger.log('valueToSearchFor: ' + valueToSearchFor)
dataFromColumnToMatch = sh.getRange(1, columnWithUniqueIdentifier, lastRow-1, 1).getValues();
dataFromColumnToMatch = dataFromColumnToMatch.toString().split(",");
//Logger.log('dataFromColumnToMatch: ' + dataFromColumnToMatch)
rowWithExistingUniqueValue = dataFromColumnToMatch.indexOf(valueToSearchFor);
//Logger.log('rowWithExistingUniqueValue: ' + rowWithExistingUniqueValue)
if (rowWithExistingUniqueValue === -1) {//There is no existing data with the unique identifier
return;
}
sh.getRange(rowWithExistingUniqueValue + 1, 1, 1, rowOfDataJustSaved[0].length).setValues(rowOfDataJustSaved);
sh.deleteRow(lastRow);//delete the row that was at then end
}