PowerQuery COUNTIF Previous Dates

Question

I\'m a little rusty on PowerQuery.
I need to count \"previous\" entries in the same table.

For example, let\'s say we have a table of car sales.
For the purposes

Answer 1

You can do this sort of thing using List and Table functions. I'll show both.

let
    Source = Excel.CurrentWorkbook(){[Name="tblCarSales"]}[Content],
    #"Added Custom" = Table.AddColumn(Source, "Previous Sale Count",
                         (C) => List.Count(List.Select(Source[Sale Date],
                                each _ < C[Sale Date]))),
    #"Added Custom1" = Table.AddColumn(#"Added Custom", "Previous Sale Count By Make",
                         (C) => Table.RowCount(Table.SelectRows(Source,
                                (S) => S[Sale Date] < C[Sale Date] and S[Make] = C[Make])))
in
    #"Added Custom1"

We have to use the functions so that Power Query knows what context we're looking at the columns in. For further reading, check out this Power Query M Primer.