Google-sheets – Delete Duplicate Rows Based on 1 Column

google sheetsgoogle-apps-script

I am looking for a Google Sheets script that will delete anything after the first instance of a duplicate row but only search column B. I found the following script on here but it only addresses duplicate rows that are back to back. For example if cell B5, B7, and B15 all had the same content I would like it to deleted Row 7 and Row 15. Any help is much appreciated.

function removeDuplicates() {
  var sheet = SpreadsheetApp.getActiveSheet();
  var rows = sheet.getLastRow();
  var firstColumn = sheet.getRange(2, 2, rows, 1).getValues();
  for (var i = rows; i >= 2; i--) {
    if (firstColumn[i-1][0] == firstColumn[i-2][0]) {
      sheet.deleteRow(i);
    }
  }
}

Best Answer

Try changing from 

var firstColumn = sheet.getRange(2, 2, rows, 1).getValues();
  for (var i = rows; i >= 2; i--) {
    if (firstColumn[i-1][0] == firstColumn[i-2][0]) {
      sheet.deleteRow(i);

To

var firstColumn = sheet.getRange(1, 2, rows, 1).getValues();
firstColumn = firstColumn.map(function (e) {return e[0]})
  for (var i = rows; i >0; i--) {
    if (firstColumn.indexOf(firstColumn[i-1]) != i-1) {
      sheet.deleteRow(i);
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