Index column based on value/category

Anonymous - See this. You can do this 100% through the user interface. It works with any number of columns.

1. Group your table by the desired column you want the index based on. For the aggregation, type "All Rows" for the column name and then "All Rows" in the operation.
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2. Add the Index column.
3. CLick on the expansion button for the All Rows column and expand ALL columns except the one you based the index on.
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4. End result:
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let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45W8ixJzVVwVNJRMgZiE6VYHSQhEyC2QAg5AblmQGyKKgTSaGiAKmYOVoqhzBgh5Aw2CGxYLAA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Column 1" = _t, Test1 = _t, Test2 = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Test1", Int64.Type}, {"Test2", Int64.Type}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"Column 1"}, {{"All Rows", each _, type table [Column 1=nullable text, Test1=nullable number, Test2=nullable number]}}),
    #"Added Index" = Table.AddIndexColumn(#"Grouped Rows", "Index", 1, 1, Int64.Type),
    #"Expanded All Rows" = Table.ExpandTableColumn(#"Added Index", "All Rows", {"Test1", "Test2"}, {"Test1", "Test2"})
in
    #"Expanded All Rows"

  How to use M code provided in a blank query:
1) In Power Query, select New Source, then Blank Query
2) On the Home ribbon, select "Advanced Editor" button
3) Remove everything you see, then paste the M code I've given you in that box.
4) Press Done
5) See this article if you need help using this M code in your model.