How to count consecutive date ranges in Power Query M?

[Mike1983]

Hello! Hopefully someone can help me!

I have a table of absence start and end dates (300k rows). Where absences are consecutive (previous end date is the day before the next start date), I want to capture the first of the consecutive dates in that series as Consecutive Abs Start. It could be any number of absences in a consecutive series. Please see the desired result below. I want to do this in PowerQuery M (instead of PowerBI DAX front end) so I can use the result further in my transformations.

If anyone can help me that would be great! Thanks.  Mike

Person	Abs Start	Abs End	Consecutive Abs Start (desired result)
20000001	01.01.2024	02.01.2024	01.01.2024
20000001	15.01.2024	17.01.2024	15.01.2024
20000001	18.01.2024	19.01.2024	15.01.2024
20000001	20.01.2024	20.01.2024	15.01.2024
20000001	21.01.2024	21.01.2024	15.01.2024
20000001	22.01.2024	22.01.2024	15.01.2024
20000001	23.01.2024	23.01.2024	15.01.2024
20000001	01.02.2024	01.02.2024	01.02.2024
20000001	15.02.2024	15.02.2024	15.02.2024
20000001	16.02.2024	16.02.2024	15.02.2024
20000001	01.03.2024	01.03.2024	01.03.2024

[dufoq3 · Accepted solution]

Hi @Mike1983,

Result:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("ddDRCoAgDIXhd/FaYjuW1bOI7/8atgg7jSbe/PDBdK0lyH005SS6XBeC1QIzev4w3YjpHrKD2RkxCDEKz/htFJ6BWfgFFGYlYrYQzIW88bOQySg8q8xqxGxO4aFP9D4A", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Person = _t, #"Abs Start" = _t, #"Abs End" = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Abs Start", type date}, {"Abs End", type date}}, "sk-SK"),
    #"Added Index1" = Table.AddIndexColumn(#"Changed Type", "IndexHelper", 0, 1, Int64.Type),
    #"Added Dates" = Table.AddColumn(#"Added Index1", "Dates", each List.Dates([Abs Start], Duration.TotalDays([Abs End] - [Abs Start])+1, #duration(1,0,0,0)), type list),
    #"Expanded Dates" = Table.ExpandListColumn(#"Added Dates", "Dates"),
    #"Added Index" = Table.AddIndexColumn(#"Expanded Dates", "Index", 0, 1, Int64.Type),
    #"Grouped Rows" = Table.Group(#"Added Index",
        {"Person", "Dates", "Index"}, { {"All", each _, type table}, {" Consecutive Abs Start", each List.Min([Dates]), type date}},
        GroupKind.Local,
        (s,c)=> Byte.From(c[Index]-s[Index] <> Duration.Days(c[Dates]-s[Dates]))),
    #"Expanded All" = Table.ExpandTableColumn(#"Grouped Rows", "All", {"Abs Start", "Abs End", "IndexHelper"}, {"Abs Start", "Abs End", "IndexHelper"}),
    #"Removed Duplicates" = Table.Distinct(#"Expanded All", {"IndexHelper"}),
    #"Removed Columns" = Table.RemoveColumns(#"Removed Duplicates",{"IndexHelper", "Dates", "Index"})
in
    #"Removed Columns"

[Mike1983]

Fantastic, thank you. I got there in the end but I used about 10 times as many steps, this is certainly much more elegant. 

[dufoq3]

You're welcome Mike. Enjoy. Don't forget that your data needs to be sorted by Abs Start.