Select a value from minimum and maximum date by group

Ah so you need the score at each of the dates?  What if there are multiple rows for each group and date? I would also use different column names (like "Score at Date min"  for example) to reduce the potential for misinterpretation.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjDU9UrM0zUyUdJRcgRiM3MLpVgdoLiRrltqEkLc2MQUIm6s659cghA3NLKEiJsizHECYlMDA7C4oYWub2IRQtwEJm6o65dfhhA3BonHAgA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Date = _t, Group = _t, Score = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Date", type date}, {"Score", Int64.Type}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"Group"}, {{"Date min", each List.Min([Date]), type nullable date}, {"Date max", each List.Max([Date]), type nullable date}, {"Rows", each _, type table [Date=nullable date, Group=nullable text, Score=nullable number]}}),
    #"Added Custom" = Table.AddColumn(#"Grouped Rows", "Score min", each Table.SelectRows([Rows], (k)=> k[Date]=[Date min])[Score]{0},Int64.Type),
    #"Added Custom1" = Table.AddColumn(#"Added Custom", "Score max", each Table.SelectRows([Rows], (k)=> k[Date]=[Date max])[Score]{0},Int64.Type)
in
    #"Added Custom1"

Thanks for the reply from lbendlin , please allow me to provide another insight:
Hi  CornelisV ,

Here are the steps you can follow：

1. Create calculated table.

Test_Table =
var _table1=
ADDCOLUMNS(
    'Table',
    "Date min",
    MINX(FILTER('Table',[Group]=EARLIER([Group])),[Date]),
    "Date max",
    MAXX(FILTER('Table',[Group]=EARLIER([Group])),[Date]))
return
SUMMARIZE(
    _table1,[Date min],[Date max],[Group],
    "Score min",SUMX(FILTER(_table1,[Date]=EARLIER([Date min])),[Score]),
    "Score max",SUMX(FILTER(_table1,[Date]=EARLIER([Date max])),[Score]))

2. Result:

Best Regards,

Liu Yang

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