Filter outlier data rows from a data table in power bi

myti What is the source of your data? And this sounds like something you would want to do on the import side of things, so i'd recommend you try to get some feedback from ImkeF, she's the master of "M" related solutions.

myti: You shouldn't mark your question as answered: If @Eno1978 Eno hadn't posted me in I wouldn't have looked at it :-)

Fortunately, there is a function for Standard Deviation in M already. But you need a trick in order to apply it to the needed list / to create the lists with different length. Therefore you add an Index-column after you sorted your values. Then you create the lists by specifying all values from the column up to the current row. So your code would look like this:

let
    Source = Excel.CurrentWorkbook(){[Name="Tabelle2"]}[Content],
    #"Sorted Rows" = Table.Sort(Source,{{"List", Order.Ascending}}),
    #"Added Index" = Table.Buffer(Table.AddIndexColumn(#"Sorted Rows", "Index", 0, 1)),
    #"Added Custom" = Table.AddColumn(#"Added Index", "Custom", each List.StandardDeviation({#"Added Index"[List]{0}..#"Added Index"[List]{[Index]}}))
in
    #"Added Custom"

Where "Tabelle2" is the source-table with column "List" with the values to sort.