True Unduplicated

Hi TuckRhodes ,

Thank you for the detailed explanation!
You need to have an Index column to identify the first time the ID appears, like this:

Considering you mentioned that your data is huge, I would recommend doing this in Power Query to prevent possible performance and memory issues:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WcnYMMVTSUQr28HcNBtKGSrE6CEF/Z2+QoBFM0Ais0jMoBEgbIwsGOPqFgFSaIGtHEowFAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [CATEGORY = _t, ITEM = _t, ID = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"CATEGORY", type text}, {"ITEM", type text}, {"ID", Int64.Type}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"ID"}, {{"Count", each Table.AddIndexColumn(_, "Index", 1, 1, Int64.Type)}}),
    #"Expanded Count" = Table.ExpandTableColumn(#"Grouped Rows", "Count", {"CATEGORY", "ITEM", "Index"}, {"CATEGORY", "ITEM", "Index"}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Expanded Count",{{"Index", Int64.Type}})
in
    #"Changed Type1"

Put all of the M code into the Advanced Editor:

And click "Close & Apply":

Then use this DAX to create a measure:

Count_Chart = 
CALCULATE(
    DISTINCTCOUNT('Table'[ID]),
    'Table'[Index] = 1
)

And the final output is as below:

Best Regards,
Dino Tao
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