Arcade Expression - Calculate Field - Reorganizing data within a field

[Roose_22]

I'm creating a grid index for roads. I've created the field (Page:Grid) and it includes the page number and grid number, but they are listed as such: 

I'd like the data to display with the page number then all grids on that particular page. So rather than reading 26: C1, 26: C2, 26: C3, 26: C4 it would appear 26: C1, C2, C3, C4. I was thinking calculate field would be the best way to reorganize the field the way I'd like. Is this possible?

[Robert_Houston]

Does the following calculate field script produce the output you'd like? Be sure to enable Edit Undo! You might need to change the $feature['x'] names to match your fields.

var pagenum = $feature['Page Number'] + ":"
pagenum + Concatenate(Split($feature['Page:Grid'],pagenum))

[Roose_22]

Thanks, Robert! It did for some records, but not all for some reason.  I'm not sure if the attached image is ledgable or not. The field showing 39: A3,39: A4,39: A5,39: B2,39: B3,39: C2,38: E4,38: E5,42: B1,42: C1 produced results of 39: A3, A4, A5, B2, B3, C2,38: E4,38: E5,42: B1,42: C1 with the provided script. I created a new field named Index for the calculate field results to populate. 

[KenBuja · Accepted solution]

This should give you the correct output

var arrField = Split($feature['Page:Grid'],",");
var dict = {}
for (var i in arrField) {
  var input = Split(arrField[i], ": ");
  var key = input[0];
  if (HasKey(dict, key)) {
    var value = Concatenate([dict[key], input[1]], ", ")
    dict[key] = value;
  } else {
    dict[key] = input[1]
  }
}
var output = [];
for (var k in dict) {
  Push(output, Concatenate([k, dict[k]], ': '))
}
return Concatenate(output, ' | ')

For example, this would return "20: E5 | 21: A5 | 22: A1 | 26: D1, E1" for row 8

[Roose_22]

Thank you!!