Power Query Assign group identification every n number of elements

Question

I have a CSV file that I need to import with PowerQuery. I want to assign groups of 3 and give them a name or room number. I know it is possible to use the Table.FillUp function to fill the values up. But I don't know how to assign a variable or another method to change the classroom identification

Parts of M code

#"Added Index" = Table.AddIndexColumn(Source, "Fila", 1, 1, Int64.Type),
#"Added Custom" = Table.AddColumn(#"Added Index", "CadaV3", each if Number.Mod([Fila], 3)=0 then 1 else 0)

Answer 1

If your student IDs are consecutive, per your example, then you can use Number.IntegerDivide:

#"Added Room Number" = Table.AddColumn(#"Previous Step", "Room Number", each Number.IntegerDivide([studentId] - 1,3))

Alternatively, add an Index column, and use that similarly:

#"Added Index" = Table.AddIndexColumn(#"Previous Step", "Index", 1, 1, Int64.Type),
#"Added Room Number" = Table.AddColumn(#"Added Index", "Room Number", each Number.IntegerDivide([Index] - 1,3))

Answer 2

Depending on only the assign groups of 3 direction, with no dependency on Student ID or Index columns:

good for up to 26 classrooms -- if it might be more, we need a different approach

et
    Source = Excel.CurrentWorkbook(){[Name="Students"]}[Content],

//generate a list of classrooms "by threes"
    classRooms = List.Transform(
        List.Range(
            List.Sort(
                List.Repeat({1..
                    Number.RoundAwayFromZero(Table.RowCount(Source)/3,0)},3)),
            0,Table.RowCount(Source)), each Character.FromNumber(_+64)),

//add the classroomID column
    roomAssignment = Table.FromColumns(
        Table.ToColumns(Source) & {classRooms},
        type table[StudentID=Int64.Type, Name=text, ClassroomID=text])
   
in
    roomAssignment