Incrementing index on multiple categories - Power Query M

Hi Anonymous 

I am not sure if I made it too complicated, but it got what you want:

let
Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WclTSUfLMUwgoyk8vSi0uVorVIU3MOT+3ICe1JDWFBjpdsIi5YhFzwyGGagOGqlgA", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [ID = _t, Status = _t]),
#"Added Index" = Table.AddIndexColumn(Source, "SortIndex", 0, 1, Int64.Type),
GroupToDiff = Table.Group(#"Added Index", {"ID", "Status"}, {{"Table", each _, type table }}),
AddTest = Table.AddColumn(GroupToDiff, "Custom", each if [Status] = "Completed" then Table.AddIndexColumn([Table],"test",1,1) else Table.AddColumn([Table], "test", each 0)),
SelectCustom = Table.SelectColumns(AddTest,{"Custom"}),
#"Expanded Custom" = Table.ExpandTableColumn(SelectCustom, "Custom", {"ID", "Status", "SortIndex", "test"}, {"ID", "Status", "SortIndex", "test"}),
#"Sorted Rows" = Table.Sort(#"Expanded Custom",{{"SortIndex", Order.Ascending}}),
#"Grouped Rows" = Table.Group(#"Sorted Rows", {"ID"}, {{"allrows", each _, type table }}),
#"Added Custom" = Table.AddColumn(#"Grouped Rows", "Custom", (OT)=> Table.AddColumn(OT[allrows],"new",
(x)=>[a=List.Min( List.Select( Table.SelectColumns( Table.SelectRows(OT[allrows],(IT)=> IT[SortIndex]>=x[SortIndex]),"test")[test], each _ <>0)),
b=List.Max( List.Select( Table.SelectColumns( Table.SelectRows(OT[allrows],(IT)=> IT[SortIndex]<=x[SortIndex]),"test")[test], each _ <>0)),
c=if a <>null then a else if b<>null then b+1 else 0][c])),
#"Added Custom1" = Table.AddColumn(#"Added Custom", "final", each Table.Group([Custom],{"ID","new"},{{"t", each _,type table}})),
#"Removed Other Columns" = Table.SelectColumns(#"Added Custom1",{"final"}),
#"Expanded final" = Table.ExpandTableColumn(#"Removed Other Columns", "final", {"t"}, {"t"}),
#"Added Custom2" = Table.AddColumn(#"Expanded final", "Custom", each Table.AddIndexColumn([t],"Index",1,1)),
#"Removed Other Columns1" = Table.SelectColumns(#"Added Custom2",{"Custom"}),
#"Expanded Custom1" = Table.ExpandTableColumn(#"Removed Other Columns1", "Custom", {"ID", "Status", "SortIndex", "Index"}, {"ID", "Status", "SortIndex", "Index"})

in
#"Expanded Custom1"

Hello Anonymous 

as I can see the index has to restart whenever ID and status together are changing. So you need to apply Table.Group with GroupKind.Local. This grouped tables then get a Index column starting with 1 by applying a Table.TransformColumns. By the way I was assuming that ID and status are two different columns and therefore I splittet your data into two different columns.

Here the complete code

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WclTwzFMIKMpPL0otLlaK1SFWxDk/tyAntSQ1hWg9Tmh6nDFUuGCIuGKIuKGZgslH0RELAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [ID = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"ID", type text}}),
    #"Split Column by Delimiter" = Table.SplitColumn(#"Changed Type", "ID", Splitter.SplitTextByEachDelimiter({" "}, QuoteStyle.Csv, false), {"ID.1", "ID.2"}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Split Column by Delimiter",{{"ID.1", type text}, {"ID.2", type text}}),
    #"Renamed Columns" = Table.RenameColumns(#"Changed Type1",{{"ID.1", "ID"}, {"ID.2", "Status"}}),
    #"Grouped Rows" = Table.Group(#"Renamed Columns", {"ID", "Status"}, {{"AllRows", each _, type table [ID=text, Status=text]}}, GroupKind.Local),
    AddIndexToTable = Table.TransformColumns
    (
        #"Grouped Rows",
        {
            {
                "AllRows",
                (tbl)=> Table.AddIndexColumn(tbl,"Index", 1)
            }
        }
    ),
    #"Expanded AllRows" = Table.ExpandTableColumn(AddIndexToTable, "AllRows", {"Index"}, {"Index"})
in
    #"Expanded AllRows"

Copy paste this code to the advanced editor in a new blank query to see how the solution works.
If this post helps or solves your problem, please mark it as solution (to help other users find useful content and to acknowledge the work of users that helped you)
Kudoes are nice too

Have fun

Jimmy