Conditional Simple Moving Average

Hi, Jan-Jaap72 

According to your M code , it seems you want to get the average of the  previous_3_row values in for the [adj_close] column.

And for your M code , you create mult-table and columns in it .

For your need , you can try to use this M code to see if there is a improvement for performance.

let
Source = Excel.Workbook(File.Contents("C:\test.xlsx"), null, true),
 Table1_Table = Source{[Item="Table1",Kind="Table"]}[Data],
    #"Promoted Headers" = Table.PromoteHeaders(Table1_Sheet, [PromoteAllScalars=true]),
       #"Changed Type" = Table.TransformColumnTypes(#"Promoted Headers",{{"ticker", type text}, {"date", type date}, {"open", type number}, {"high", type number}, {"low", type number}, {"close", type number}, {"volume", Int64.Type}, {"dividend", type number}, {"split", Int64.Type}, {"adj_open", type number}, {"adj_high", type number}, {"adj_low", type number}, {"adj_close", type number}, {"adj_volume", Int64.Type}}),
    Custom1 = Table.Group(#"Changed Type","ticker",{"test",(x)=>   Table.AddIndexColumn( x, "Index", 1, 1, Int64.Type)      }),
    #"Expanded test" = Table.ExpandTableColumn(Custom1, "test", {"date", "open", "high", "low", "close", "volume", "dividend", "split", "adj_open", "adj_high", "adj_low", "adj_close", "adj_volume", "Index"}, {"date", "open", "high", "low", "close", "volume", "dividend", "split", "adj_open", "adj_high", "adj_low", "adj_close", "adj_volume", "Index"}),
    #"Added Custom" = Table.AddColumn(#"Expanded test", "Custom", (x)=>  
try List.Average( List.Range(#"Expanded test"[adj_close],x[Index]-3,3)) otherwise null
)
,
    #"Changed Type1" = Table.TransformColumnTypes(#"Added Custom",{{"date", type date}, {"open", type number}, {"high", type number}, {"low", type number}, {"close", type number}, {"volume", Int64.Type}, {"dividend", type number}, {"split", Int64.Type}, {"adj_open", type number}, {"adj_high", type number}, {"adj_low", type number}, {"adj_close", type number}, {"adj_volume", Int64.Type}, {"Custom", type number}, {"Index", Int64.Type}})
in
    #"Changed Type1"

Then we can get this in the Power Query Editor:

And also we can keep the Index column and apply the data to the Desktop and we can click "New Column" to create a calculated column :

Column = var _t = FILTER('Query1' , 'Query1'[ticker] = EARLIER('Query1'[ticker]) && 'Query1'[Index]<=EARLIER(Query1[Index]) && 'Query1'[Index]>EARLIER(Query1[Index])-3)

return
AVERAGEX(_t ,[adj_close])

We can also get this in Desktop:

If this method does not meet your needs, you can provide us with your special sample data and the desired output sample data in the form of tables, so that we can better help you solve the problem. (You can also upload you sample .pbix [without sensitive data] to the OneDrive and share with the OneDrive link to me ! )

Thank you for your time and sharing, and thank you for your support and understanding of PowerBI! 

Best Regards,

Aniya Zhang

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