Find previous event in an event log using Power Query

Hello magnus_b 

 

You can group your data applying the function of the whole table. Then with a Table.TransformColumns you can manipulate the grouped table by sorting it, adding index column and then adding a new column, where the grouped table is filtered by [Index]-1.

here a praticable example (in case, substitue the source and the changes-type step with your existing query

 

 

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("hc/NCoNADATgVyk5iySzq2bzKosHaZdSKLW4pc9v8GZ/r8NHJpMzpQRVagjaCrdg8IHVus4CPD0uZXqUE41NpkHQhxeZDPouP910mYzZ06nWy/n2kwan0dM6X5/f24UtRmPsoQ6y1eyhD2L5P0jEAIu9p0uZ72V7c1wB", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [case_id = _t, timestamp = _t, event = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"case_id", Int64.Type}, {"timestamp", type datetime}, {"event", type text}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"case_id"}, {{"AllRows", each _, type table [case_id=number, timestamp=datetime, event=text]}}),
    SortAndAddColumn = Table.TransformColumns
    (
        #"Grouped Rows",
        {
            {
                "AllRows",
                (tbl)=> let 
                    Sort = Table.Sort(tbl, {{"timestamp", Order.Ascending}}),
                    Index = Table.AddIndexColumn(Sort, "Index"),
                    AddPrevious= Table.AddColumn(Index, "Previous", (row)=> try Table.SelectRows(Index, each [Index]= row[Index]-1)[event]{0} otherwise "")
                    in 
                    AddPrevious
            }
        }
    ),
    #"Expanded AllRows" = Table.ExpandTableColumn(SortAndAddColumn, "AllRows", {"timestamp", "event", "Previous"}, {"timestamp", "event", "Previous"}),
    #"Sorted Rows" = Table.Sort(#"Expanded AllRows",{{"timestamp", Order.Ascending}})



in
    #"Sorted Rows"

 

 

Copy paste this code to the advanced editor in a new blank query to see how the solution works

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Kudoes are nice too

Have fun

Jimmy

 

Given the limitations of direct query, you may need to do this in a measure.  How do you plan to use this column once generated?  If it will just be a value in a table/matrix, then a measure would work.  If it will be used as a legend or on an axis, a column is needed.

 

Regards,

Pat