End date based on next row (Index+1) for each row

Hi mthiru, there are many ways. This one is not easy to understand, but it is realy fast.

Result

let
    fnShift = (tbl as table, col as text, shift as nullable number, optional newColName as text) as table =>
        //v 3. parametri zadaj zaporne cislo ak chces posunut riadky hore, kladne ak dole, 4. je nepovinny (novy nazov stlpca)
        let
            a = Table.Column(tbl, col),
            b = if shift = 0 or shift = null then a else if shift > 0
                then List.Repeat({null}, shift) & List.RemoveLastN(a, shift)
                else List.RemoveFirstN(a, shift * -1) & List.Repeat({null}, shift * -1),    
            c = Table.FromColumns(Table.ToColumns(tbl) & {b}, Table.ColumnNames(tbl) &
                ( if newColName <> null then {newColName} else
                    if shift = 0 then {col & "_Duplicate"} else
                    if shift > 0 then {col & "_PrevtValue"} 
                    else              {col & "_NextValue"} ))
        in
        c,
    
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMtc31jcyMLRQitUBcwwRPAt9VI4JgmeJLGVoAOfFAgA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Start Date" = _t]),
    ChangedType = Table.TransformColumnTypes(Source,{{"Start Date", type date}}, "en-US"),
    Ad_StartDateNextValue = fnShift(ChangedType, "Start Date", -1),
    Ad_EndDate = Table.AddColumn(Ad_StartDateNextValue, "End Date", each if Date.ToText([Start Date], [Format = "yyyy-MM"]) = Date.ToText([Start Date_NextValue], [Format = "yyyy-MM"]) then Date.AddDays([Start Date_NextValue], -1) else Date.EndOfMonth([Start Date]), type date),
    RemovedColumns = Table.RemoveColumns(Ad_EndDate,{"Start Date_NextValue"})
in
    RemovedColumns