Group by the last two dates

Hi,

this will sort the data by [Position ID] and [Date] and only keep the last two dates for each position id:

let
  Source = Table.FromRows(
    Json.Document(
      Binary.Decompress(
        Binary.FromText(
          "nZJNC4JAEIb/yuI5Y2b2K+fatTpUdBEPgVIdTJAi+veNZpAG4nZbFh7ed56ZNI0OSwLCGIF0NIvkbWJwMaFCx9Yywhzkf1sc86faVI8om30xrseAQmByDEnL7M5VfVP7oi77kPeDIGRYfIJW1fU0jZF+BltmXeSXezmR0mxMAIW+ocizduFUwvhHQ6FssECRQZMFvutpy3a69I4xrH2ICKfQMlk2ozch1zeIosY5jW+qT3UiRKAfGeqXAbZa5gpI6rYryt0wKXsB", 
          BinaryEncoding.Base64
        ), 
        Compression.Deflate
      )
    ), 
    let
      _t = ((type nullable text) meta [Serialized.Text = true])
    in
      type table [#"Position ID" = _t, Date = _t, Availability = _t]
  ), 
  inputTable = Table.TransformColumnTypes(Source, {{"Position ID", type text}, {"Date", type datetime}, {"Availability", type text}}), 
  inputTableSorted = Table.Sort(inputTable, {{"Position ID", Order.Descending}, {"Date", Order.Descending}}), 
  #"Added Custom" = Table.AddColumn(
    inputTableSorted, 
    "RowsForPositionID", 
    (outerRow) => Table.SelectRows(inputTableSorted, (innerRow) => innerRow[Position ID] = outerRow[Position ID])
  ), 
  #"Added Custom1" = Table.AddColumn(#"Added Custom", "Max2Dates", each List.MaxN([RowsForPositionID][Date], 2)), 
  #"Added Custom2" = Table.AddColumn(#"Added Custom1", "IsInLastTwoDates", each if List.Contains([Max2Dates], [Date]) then true else false), 
  #"Filtered Rows" = Table.SelectRows(#"Added Custom2", each ([IsInLastTwoDates] = true)), 
  #"Removed Columns" = Table.RemoveColumns(#"Filtered Rows", {"RowsForPositionID", "Max2Dates", "IsInLastTwoDates"}), 
  tableSorted = Table.Sort(#"Removed Columns", {{"Position ID", Order.Descending}, {"Date", Order.Descending}})
in
  tableSorted

Or a more elegant solution with using Table.MaxN:

let
  Source = Table.FromRows(
    Json.Document(
      Binary.Decompress(
        Binary.FromText(
          "nZJNC4JAEIb/yuI5Y2b2K+fatTpUdBEPgVIdTJAi+veNZpAG4nZbFh7ed56ZNI0OSwLCGIF0NIvkbWJwMaFCx9Yywhzkf1sc86faVI8om30xrseAQmByDEnL7M5VfVP7oi77kPeDIGRYfIJW1fU0jZF+BltmXeSXezmR0mxMAIW+ocizduFUwvhHQ6FssECRQZMFvutpy3a69I4xrH2ICKfQMlk2ozch1zeIosY5jW+qT3UiRKAfGeqXAbZa5gpI6rYryt0wKXsB", 
          BinaryEncoding.Base64
        ), 
        Compression.Deflate
      )
    ), 
    let
      _t = ((type nullable text) meta [Serialized.Text = true])
    in
      type table [#"Position ID" = _t, Date = _t, Availability = _t]
  ), 
  inputTable = Table.TransformColumnTypes(Source, {{"Position ID", type text}, {"Date", type datetime}, {"Availability", type text}}), 
  inputTableSorted = Table.Sort(inputTable, {{"Position ID", Order.Descending}, {"Date", Order.Descending}}),
    #"Grouped Rows" = Table.Group(inputTableSorted, {"Position ID"}, {{"Filtered", each Table.MaxN(_,"Date",2)}}),
    #"Expanded Filtered" = Table.ExpandTableColumn(#"Grouped Rows", "Filtered", {"Date", "Availability"}, {"Filtered.Date", "Filtered.Availability"}),
    #"Renamed Columns" = Table.RenameColumns(#"Expanded Filtered",{{"Filtered.Date", "Date"}, {"Filtered.Availability", "Availability"}}),
    tableSorted = Table.Sort(#"Renamed Columns", {{"Position ID", Order.Descending}, {"Date", Order.Descending}})
in
    tableSorted