Finding First Result using Date & Unique ID

If your data is guaranteed to be sorted by Unique ID and Date (Ascending) as you show in your example, then:

• Group by Unique ID
• Extract the first Grade Value
• Re-expand the table

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("bY7BDcAgDAN3yRspiUOomAWx/xptilSKlIdfZ588Bqn3RoX8iSirMASgWT4SgbAiJeosL7FFWg1TTWyLWGz6adsbtdN2IfpIbJv8v80b", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Unique ID" = _t, #"Grade Value" = _t, #"Result Date" = _t]),
    
    #"Changed Type" = Table.TransformColumnTypes(Source,{
        {"Unique ID", Int64.Type}, {"Grade Value", Int64.Type}, {"Result Date", type date}}, "en-GB"),

//Add index value to force Table.Group to maintain sort order
    #"Added Index" = Table.AddIndexColumn(#"Changed Type", "Index", 0, 1, Int64.Type),
    
    #"Grouped Rows" = Table.Group(#"Added Index", {"Unique ID"}, {
        {"all", each _, type table [Unique ID=nullable number, Grade Value=nullable number, Result Date=nullable date, Index=number]},
        {"First Grade Value", each [Grade Value]{0}, Int64.Type}}),
    #"Expanded all" = Table.ExpandTableColumn(#"Grouped Rows", "all", {"Grade Value", "Result Date"})
in
    #"Expanded all"

If your data is NOT sorted, then you will need to add a sort step.

Hi,

select the column and FillDown