Transform data like two row with main title and subtitle ?

Hello utgqw 

here another approach. It uses List.Generate to create a new column that identifies the main groups. In the Group-function the first row is deleted and a new column with the main-cat is added

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WcgQCJR0lQwMDpVidaKXE4pQ0INcYGw/CMYFwnIAAyDOC6itOBEvCjClPLQLyTJH1gTixAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Cat = _t, Column1 = _t]),
    ChangedType = Table.TransformColumnTypes(Source,{{"Cat", type text}, {"Column1", Int64.Type}}),
    GenerateGroupColumns = List.Generate
    (
        ()=> [RunningTotal = ChangedType[Column1]{0}, Counter=0, Group=1],
        each [Counter]<= Table.RowCount(ChangedType)-1,
        (rec)=>
        [
            RunningTotal = if rec[RunningTotal] - ChangedType[Column1]{rec[Counter]+1}< 0 then ChangedType[Column1]{rec[Counter]+1} else rec[RunningTotal] - ChangedType[Column1]{rec[Counter]+1},
            Counter = rec[Counter]+1,
            Group = if rec[RunningTotal] - ChangedType[Column1]{rec[Counter]+1}< 0 then rec[Group]+1 else rec[Group]
        ],
        each [Group]
    ),
    CreateTable = Table.FromColumns(Table.ToColumns(ChangedType)&{GenerateGroupColumns}, Table.ColumnNames(ChangedType)&{"Group"}),
    GroupedRows = Table.Group
    (
        CreateTable, 
        {"Group"}, 
        {
            {
                "AllRows", 
                (tbl)=> Table.AddColumn(Table.Skip(tbl,1), "Main", each tbl[Cat]{0})
            }
        }
    ),
    RemovedOtherColumns = Table.SelectColumns(GroupedRows,{"AllRows"}),
    ExpandedAllRows = Table.ExpandTableColumn(RemovedOtherColumns, "AllRows", {"Cat", "Column1", "Group", "Main"}, {"Cat", "Column1", "Group", "Main"})
in
    ExpandedAllRows

Copy paste this code to the advanced editor in a new blank query to see how the solution works.

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Have fun

Jimmy