Nested Index Column & Referencing Previous Row

Hi thampton 

You may create two calculated columns as below:

Desired Index =
CALCULATE (
    DISTINCTCOUNT ( 'Table'[Action] ),
    FILTER ( 'Table', 'Table'[Sequence] <= EARLIER ( 'Table'[Sequence] ) )
) - 1

Duration =
DATEDIFF (
    CALCULATE (
        MAX ( 'Table'[Date Time] ),
        FILTER ( 'Table', 'Table'[Sequence] = EARLIER ( 'Table'[Sequence] ) - 1 )
    ),
    'Table'[Date Time],
    MINUTE
) + 0

Regards,

thampton 

Check the M / Power Query solution as well

File attached as well

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45W8srPyFPSUXIEYgUTYx0TMzM9AxNDMxAwVwAKGijF6sBVOSGrsjCGAJAqQ2RVzocWIKkzNDI1AAOQOiN86ixMzI2AAKTOGFmdC7IqMzOE20yUYmMB", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [User = _t, Action = _t, #"Date Time" = _t, Sequence = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Date Time", type number}, {"Sequence", Int64.Type}}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Changed Type",{{"Date Time", type datetime}}),
    #"Grouped Rows" = Table.Group(#"Changed Type1", {"Action"}, {{"All", each _, type table}}),
    #"Added Index" = Table.AddIndexColumn(#"Grouped Rows", "Index", 0, 1),
    #"Expanded All" = Table.ExpandTableColumn(#"Added Index", "All", {"User", "Date Time", "Sequence"}, {"User", "Date Time", "Sequence"}),
    #"Added Custom" = Table.AddColumn(#"Expanded All", "Custom", each let myuser=[User],myseq=[Sequence] in Duration.TotalMinutes(
[Date Time]-  (try Table.SelectRows(#"Expanded All",each [User]=myuser and [Sequence]=myseq-1)[Date Time]{0} otherwise [Date Time])))
in
    #"Added Custom"