Outline borders of groups of cells in google sheets.

outlineGroupsOfCells.gs

function onOpen() {
 var menu = [{name: "Borders for nonempty cells", functionName: "borders"}];
 SpreadsheetApp.getActiveSpreadsheet().addMenu("Custom", menu);
}

function borders() {
  var range = SpreadsheetApp.getActiveSheet().getRange("C2:O20");
  range.setBorder(false, false, false, false, false, false);
  var values = range.getValues();
  var borders = range.getValues();
  for (var i = 0; i < values.length; i++) {
    for (var j = 0; j < values[i].length; j++) {
      if (values[i][j] > 0) {
        var top = true
        var left = true
        var bottom = true
        var right = true
        if (i >=1 && values[i-1][j] > 0) {
          top = false
        }
        if (i < (values.length +1) && values[i+1][j] > 0) {
          bottom = false
        }
        if (j >= 1 && values[i][j-1] > 0) {
          left = false
        }
        if (j < (values[i].length +1) && values[i][j+1] > 0) {
          right = false
        }
        borders[i][j] = [ top, left, bottom, right ]
      }
    }
 }
 var vertical = true
 var horizontal = true
 for (var i = 0; i < values.length; i++) {
    for (var j = 0; j < values[i].length; j++) {
      if (values[i][j] > 0) {
        top = borders[i][j][0]
        left = borders[i][j][1]
        bottom = borders[i][j][2]
        right = borders[i][j][3]
        range.getCell(i + 1, j + 1).setBorder(top, left, bottom, right, vertical, horizontal);
      }
    }
 }
}

There's a boundary bug somewhere. The selected range needs to be at least one row more than the range to work on.