Expand Table columns based on row entries - to create a unique identifier

See the logic in the M code below. Basically this:

• Groups all data by ID
• Gets the first record based on the date. If it has duplicate IDs, it gets the first record. If not, it gets the only record.
• Remove all previous columns
• Expand the new unique and first record for each ID.

If you need further help, please provide data per the links at the bottom of this post.

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

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("XcjJCQAwCATAXvYteKcZsf82AhIQMs+pgoIQrGxigqaCTdiGT/gfsRETuZET50Vf", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [ID = _t, Date = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"ID", Int64.Type}, {"Date", type date}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"ID"}, {{"All Rows", each _, type table [ID=number, Date=date]}}),
    #"Added Custom" = Table.AddColumn(#"Grouped Rows", "Original Records", each Table.Max([All Rows], "Date")),
    #"Removed Other Columns" = Table.SelectColumns(#"Added Custom",{"Original Records"}),
    #"Expanded Original Records" = Table.ExpandRecordColumn(#"Removed Other Columns", "Original Records", {"ID", "Date"}, {"ID", "Date"})
in
    #"Expanded Original Records"

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