Group by and Concatenate Rows for Multiple Columns with Power Query

Anonymous You can use this:

let
    Source = Table.FromRows (
        Json.Document (
            Binary.Decompress (
                Binary.FromText (
                    "i45WMlTSUXKE41gdiIgTHMNEnOEYJGIEZLnAMUzEFY5jYwE=",
                    BinaryEncoding.Base64
                ),
                Compression.Deflate
            )
        ),
        let
            _t = ( ( type nullable text ) meta [ Serialized.Text = true ] )
        in
            type table [ ID = _t, Var1 = _t, Var2 = _t, Var3 = _t ]
    ),
    ChangedType = Table.TransformColumnTypes (
        Source,
        {
            { "ID", Int64.Type },
            { "Var1", type text },
            { "Var2", type text },
            { "Var3", type text }
        }
    ),
    Group = Table.Group (
        ChangedType,
        { "ID" },
        {
            {
                "Transformation",
                ( CurrentGroup ) =>
                    let
                        DataCols    = Table.RemoveColumns ( CurrentGroup, "ID" ),
                        ColumnNames = Table.ColumnNames ( DataCols ),
                        ColumnsList = Table.ToColumns ( DataCols ),
                        Combine     = List.Transform ( ColumnsList, each Text.Combine ( _, ", " ) ),
                        Result      = Table.FromRows ( { Combine }, ColumnNames )
                    in
                        Result,
                type table [
                    ID = nullable number,
                    Var1 = nullable text,
                    Var2 = nullable text,
                    Var3 = nullable text
                ]
            }
        }
    ),
    ExpandedTransformation = Table.ExpandTableColumn (
        Group,
        "Transformation",
        { "Var1", "Var2", "Var3" },
        { "Var1", "Var2", "Var3" }
    )
in
    ExpandedTransformation