Dynamically load last three months of data in dataflow

Alright. Following the example let me show you how to do it:

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WCg1W0lEyMjAyMTAyslSK1YlW8nSBiRgaG4JFgt0hIsaGRlARD2+YiKGxgVJsLAA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [COuntry = _t, Snapshotdate = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"COuntry", type text}, {"Snapshotdate", Int64.Type}}),
    #"Changed Type1" = Table.TransformColumnTypes(#"Changed Type",{{"Snapshotdate", type text}}),
    #"Changed Type2" = Table.TransformColumnTypes(#"Changed Type1",{"Snapshotdate", type date}),
    // New Code down here
    var_last3months = Date.AddMonths(List.Max(#"Changed Type2"[Snapshotdate]), -3),
    var_last3calendarmonths = Date.AddMonths(Date.StartOfMonth(List.Max(#"Changed Type2"[Snapshotdate])),-2),
    #"Filtered Rows" = Table.SelectRows(#"Changed Type2", each [Snapshotdate] >= var_last3calendarmonths)
    // New Code finishes here
in
    #"Filtered Rows"

Take a look at the last 3 lines.

I have created two variables that you can choose depending on what you mean with "last 3 months".

• var_last3months = If you want it to substract 90 days, for example consideran febrary 29th as the last day, then 3 months would be november 29th. Use this variable at the "Filtered Rows" step
• var_last3monthscalendar = If you want to keep completed months from 1 to last one since current month. Use this one, it will take from December 1st to Febrary 29th.

The Step "Filtered Rows" is the one finally filtering by last 3 months with the variable. You can filter Snapshotdate by the one you have chosen.

I hope that make sense.