Exponential Moving Average in Power Query M ?

jsflint 

Can you share the expected value based on the sample data that you have given?

You can save the  Excel file with the results in One Drive or Google Drive and share the link 

Ema 

Here it is

jsflint 

Please find attached the PBIX file below my signature with the desired results. Basically, the solution involves a recursive operation to calculate the EMA ( Exponential Moving Average in Power Query ).

There are two columns, Average and EMA.

Complete M Code:

let
  Source = Table.FromRows(
    Json.Document(
      Binary.Decompress(
        Binary.FromText(
          "VZLbbQRBCARz2e+TD5p3LNbln4Y5adnB3yVmmqJ/fy9+8xsEvl4X/Qghwwp2fV5fhIPY3BERuJEchFRIROmN9CAXB2Ua38gOSmEmS5Ib+UGVIdIobxQHGbsEdFLkIqlM7E/2Wu+hxDV5AjIdFmUIE58YvHQwJZX1d8OWD3PWkqL5jpeQTsim5jVsGSEEzEzGCC8lkZbO5bMdLydiZar8+OfYc17gHhy2tDi+xjrMsOVF4CQVz3WwvGSHJCedOfA+Qh8uO+qw5YWCoBJDdk24L+TBswGWFe3FJeMxhl2UXlz6eHMhbCtpndGmKFhSssvaZdYnypJC3YYyz4fVv4aBvOt8fT5/",
          BinaryEncoding.Base64
        ),
        Compression.Deflate
      )
    ),
    let
      _t = ((type nullable text) meta [Serialized.Text = true])
    in
      type table [Date = _t, Value = _t]
  ),
  #"Changed Type" = Table.TransformColumnTypes(
    Source,
    {{"Date", type date}, {"Value", type number}}
  ),
  Step1 = Table.AddIndexColumn(#"Changed Type", "Index", 0, 1, Int64.Type),
  Step2 = Table.AddColumn(
    Step1,
    "Average",
    each if [Index] > 6 then List.Average(List.Range(Step1[Value], _[Index] - 7, 7)) else null
  , type number),
  Step3 = Table.AddColumn(
    Step2,
    "EMA",
    each
      if [Index] > 6 then
        let
          start = List.First(List.RemoveNulls(Step2[Average])),
          vlist = List.Range(Step2[Value], 8, _[Index] - 7),
          acc = List.Accumulate(
            vlist,
            start,
            (state, current) => (current - state) * (2 / (1 + 7)) + state
          )
        in
          if [Index] = 7 then start else acc
      else
        null,
  type number )
in
    Step3