Power Query - running total that resets when values change

Question

I have been searching for a week now and cannot find a resolution to my problem. I have a table which lists the "event" and individual is in during a certain week. I want to add a column - via PowerQuery - that will count the number of weeks a person has been in that event and then resets if the event changes in the following week. For example...

Pers1	Date	Event	Weeks in Event
Pers1	12/22/2022	Consideration	1
Pers1	12/26/2022	Consideration	2
Pers1	1/05/2022	Interview	1
Pers1	1/12/2022	Consideration	1
Pers1	1/19/2022	Consideration	2
Pers1	1/26/2022	Awaiting Hire	1
Pers2	1/19/2022	Awaiting Hire	1
Pers2	1/26/2022	Awaiting Hire	2

Note how the count resets back to starting at 1 when Pers1 has their second stint of Consideration during weeks 1/12 and 1/19. Additionally, I need the solution to be smart enough to distinguish between two different individuals and uniquely count their time in an event.

This community has always come through for me. Please help!

EDIT 1: I incorporated the code provided by Ron and am receiving the following error: Expression.Error: 5 arguments were passed to function which expects between 2 and 4. Details: Pattern= Arguments=List

PQ Advanced Editor Code is below:

let
    Source = Excel.Workbook(File.Contents("C:\Location"), null, true),
    Sheet1_Sheet = Source{[Item="Sheet1",Kind="Sheet"]}[Data],
    #"Promoted Headers" = Table.PromoteHeaders(Sheet1_Sheet, [PromoteAllScalars=true]),
    #"Changed Type" = Table.TransformColumnTypes(#"Promoted Headers",{{"Pers1", type text}, {"Date", type date}, {"Event", type text}}),

//add an offset column for Pers and Event to do easy comparison with previous row
    offsetPersonEvent=Table.FromColumns(
        Table.ToColumns(#"Changed Type") 
            & {List.RemoveFirstN(#"Changed Type"[Pers1]) & {null}}
            & {List.RemoveFirstN(#"Changed Type"[Event]) & {null}},
            type table[Pers=text, Date=date,Event=text,offsetPers=text, offsetEvent=text] 
    ),

//create "grouper" column by checking where both Pers and Event change
    #"Added Index" = Table.AddIndexColumn(offsetPersonEvent, "Index", 0, 1),
    #"Added Custom" = Table.AddColumn(#"Added Index", "groups", 
        each if [Pers]=[offsetPers] and [Event]=[offsetEvent] then null else [Index]),

//remove unneeded columns, fillUp the grouper, and group by "grouper"
    #"Removed Columns" = Table.RemoveColumns(#"Added Custom",{"offsetPers", "offsetEvent", "Index"}),
    #"Filled Up" = Table.FillUp(#"Removed Columns",{"groups"}),

//Add Index column to each subtable
    #"Grouped Rows" = Table.Group(#"Filled Up", {"groups"}, {
        {"addedIndex", each Table.AddIndexColumn(_,"Weeks in Event",1,1,Int64.Type)
        , type table}}),

//Remove unneccessary columns
//  Expand the grouped tables
//  reset the data types
    #"Removed Columns1" = Table.RemoveColumns(#"Grouped Rows",{"groups"}),
    #"Expanded addedIndex" = Table.ExpandTableColumn(#"Removed Columns1", "addedIndex", {"Pers", "Date", "Event", "Weeks in Event"}, {"Pers", "Date", "Event", "Weeks in Event"}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Expanded addedIndex",{{"Pers", type text}, {"Date", type date}, {"Event", type text}, {"Weeks in Event", Int64.Type}})
    
in
    #"Changed Type1"

Answer 1

Ron's code worked with one minor tweak. For me, the following section of code was causing an error

//Add Index column to each subtable
    #"Grouped Rows" = Table.Group(#"Filled Up", {"groups"}, {
        {"addedIndex", each Table.AddIndexColumn(_,"Weeks in Event",1,1,Int64.Type)
        , type table}}),

I removed the Int64.Type parameter from the Table.AddIndexColumn and everything functioned. I've included the updated code snip-it below:

let
    Source = Excel.Workbook(File.Contents("C:\Location"), null, true),
    Sheet1_Sheet = Source{[Item="Sheet1",Kind="Sheet"]}[Data],
    #"Promoted Headers" = Table.PromoteHeaders(Sheet1_Sheet, [PromoteAllScalars=true]),
    #"Changed Type" = Table.TransformColumnTypes(#"Promoted Headers",{{"Pers1", type text}, {"Date", type date}, {"Event", type text}}),

    //add an offset column for Pers and Event to do easy comparison with previous row
    offsetPersonEvent=Table.FromColumns(
        Table.ToColumns(#"Changed Type") 
            & {List.RemoveFirstN(#"Changed Type"[Pers1]) & {null}}
            & {List.RemoveFirstN(#"Changed Type"[Event]) & {null}},
            type table[Pers=text, Date=date,Event=text,offsetPers=text, offsetEvent=text] 
    ),

    //create "grouper" column by checking where both Pers and Event change
    #"Added Index" = Table.AddIndexColumn(offsetPersonEvent, "Index", 0, 1),
    #"Added Custom" = Table.AddColumn(#"Added Index", "groups", 
        each if [Pers]=[offsetPers] and [Event]=[offsetEvent] then null else [Index]),

    //remove unneeded columns, fillUp the grouper, and group by "grouper"
    #"Removed Columns" = Table.RemoveColumns(#"Added Custom",{"offsetPers", "offsetEvent", "Index"}),
    #"Filled Up" = Table.FillUp(#"Removed Columns",{"groups"}),

    //Add Index column to each subtable
    #"Grouped Rows" = Table.Group(#"Filled Up", "groups", {
        {"addedIndex", each Table.AddIndexColumn(_,"Weeks in Event",1,1)
        , type table}}),

    //Remove unneccessary columns
    //  Expand the grouped tables
    //  reset the data types
    #"Removed Columns1" = Table.RemoveColumns(#"Grouped Rows",{"groups"}),
    #"Expanded addedIndex" = Table.ExpandTableColumn(#"Removed Columns1", "addedIndex", {"Pers", "Date", "Event", "Weeks in Event"}, {"Pers", "Date", "Event", "Weeks in Event"}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Expanded addedIndex",{{"Pers", type text}, {"Date", type date}, {"Event", type text}, {"Weeks in Event", Int64.Type}})

in
    #"Changed Type1"