Average based on column name and a date reference

Hi Anonymous ,

See if this helps you.

let
  Origen = Table.FromRows(
    Json.Document(Binary.Decompress(Binary.FromText("dcu7DcAgDIThXVyfhF+AmQWx/xrgoEhpUn3F3T8naRS2osxBIB8wSRXd0oBo2iDjSAuTTL5FoLZbRP0r+BT+Fjkauh8rI+Semz7ntQE=", BinaryEncoding.Base64), Compression.Deflate)), 
    let
      _t = ((type nullable text) meta [Serialized.Text = true])
    in
      type table [Date = _t, #"2008" = _t, #"2009" = _t, #"2010" = _t, #"2011" = _t, #"2012" = _t]
  ), 
  #"Tipo cambiado" = Table.TransformColumnTypes(Origen, {{"Date", type date}, {"2008", Currency.Type}, {"2009", Currency.Type}, {"2010", Currency.Type}, {"2011", Currency.Type}, {"2012", Currency.Type}}), 
  #"Índice agregado" = Table.AddIndexColumn(#"Tipo cambiado", "Index", 0, 1, Int64.Type), 
  #"Personalizada agregada" = Table.AddColumn(
    #"Índice agregado", 
    "4 years average", 
    each List.Average(
      {
        List.Last(List.Range(List.RemoveNulls(Table.Column(#"Índice agregado", Text.From(Date.Year([Date])))), 0, [Index] + 1)), 
        List.Last(List.Range(List.RemoveNulls(Table.Column(#"Índice agregado", Text.From(Date.Year([Date]) + 1))), 0, [Index] + 1)), 
        List.Last(List.Range(List.RemoveNulls(Table.Column(#"Índice agregado", Text.From(Date.Year([Date]) + 2))), 0, [Index] + 1)), 
        List.Last(List.Range(List.RemoveNulls(Table.Column(#"Índice agregado", Text.From(Date.Year([Date]) + 3))), 0, [Index] + 1))
      }
    ), 
    Currency.Type
  )
in
  #"Personalizada agregada"