Expression.Error: We cannot convert the value 3 to type Function.

Thank you selimovd ,

I just figured it out:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("jdE7CsMwFETRrRjVBuk9fV1KK0hvXCYQCAhi758YnCoEdMuBU91ZV+OdFbHqzGxu/X08+uvZp1rrueu+349JzDYDpox5xgJjkbHEWGasMLZcTKwoyDtiyphnLDAWGUuMZcYKY1deidadL8gg75ApY56xwFhkLDGWGSuMffOmP6y19sN0QS8MmTLmGQuMRcYSY5mxwtiZd/sA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Date = _t, Portofolio = _t, Asset = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Date", type date}}),
    #"Sorted Rows" = Table.Sort(#"Changed Type",{{"Asset", Order.Ascending},{"Date", Order.Ascending}}),
    #"Grouped Rows" = Table.Group(#"Sorted Rows", {"Asset"}, {{"t_Asset", each _, type table [Date=nullable text, Portofolio=nullable text, Asset=nullable text]}}),
    #"Added Custom" = Table.AddColumn(#"Grouped Rows", "t_Index", each Table.AddIndexColumn([t_Asset], "Index", 1, 1, Int64.Type)),
    #"Removed Columns" = Table.RemoveColumns(#"Added Custom",{"t_Asset"}),
    #"Added Custom1" = Table.AddColumn(#"Removed Columns", "Portfolio", each Table.SelectRows([t_Index],(Innertable)=> Innertable[Index] = Table.RowCount([t_Index])-1)),
    #"Removed Columns1" = Table.RemoveColumns(#"Added Custom1",{"t_Index"}),
    #"Expanded Portfolio" = Table.ExpandTableColumn(#"Removed Columns1", "Portfolio", {"Portofolio"}, {"Portofolio"})
in
    #"Expanded Portfolio"