Subtract Values in consecutive rows

let me have some doubts about this statement. In any case, for those wishing to try the different times of the two different solutions, you can use this script that I got from Ben Gribaudo's blog.

Obviously the results can vary a lot depending on many things. But you can test the performance of these scripts for different dimensions of the dataset

let

    //Get the current time, which will be the query start time
    StartTime = DateTime.LocalNow(),
    //Make sure StartTime is evaluated just before we request data from Facebook
    trig = if StartTime<>null
         then 
             #"toAndFromCols LDS"
             else
         null,
    //Find the number of rows returned
    NumberOfRows = Number.ToText(Table.RowCount(trig)),
    //Get the current time, which will be the query end time
    EndTime = DateTime.LocalNow(),
    //Make sure PQ evvaluates all expressions in the right order:
    //first, get the Number of rows, which ensure that
    //the Source expression is evaluated, and in turn StartTime is evaluated
    //second, the EndTime is evaluated as part of the duration calculation
    Output = "Query analized " & NumberOfRows & " rows and took "& Duration.ToText(EndTime - StartTime)
in
    Output

let

    //Get the current time, which will be the query start time
    StartTime = DateTime.LocalNow(),
    //Make sure StartTime is evaluated just before we request data from Facebook
    trig = if StartTime<>null
         then 
             #"listgenerate LDS"
             else
         null,
    //Find the number of rows returned
    NumberOfRows = Number.ToText(Table.RowCount(trig)),
    //Get the current time, which will be the query end time
    EndTime = DateTime.LocalNow(),
    //Make sure PQ evvaluates all expressions in the right order:
    //first, get the Number of rows, which ensure that
    //the Source expression is evaluated, and in turn StartTime is evaluated
    //second, the EndTime is evaluated as part of the duration calculation
    Output = "Query analized " & NumberOfRows & " rows and took " & Duration.ToText(EndTime - StartTime)
in
    Output

listGenerate LDS:

let
    Source = LDS,// Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
     
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"DATETIME", type datetime}, {"CATEGORY", type text}, {"CUMULATIVE VIEWS", Int64.Type}}),
    #"Sorted Rows" = Table.Buffer(Table.Sort(#"Changed Type",{{"CATEGORY", Order.Ascending}, {"DATETIME", Order.Ascending}})),
    listCategory = List.Buffer(#"Sorted Rows"[CATEGORY]),
    listCumulative = List.Buffer(#"Sorted Rows"[CUMULATIVE VIEWS]),
    listCount = List.Count(listCategory),
    listCumulativeDifference =
        List.Skip(
            List.Generate(
                ()=> [varCategory = listCategory{0}, varDiff = 0, Counter = 0],
                each [Counter] <= listCount,
                each 
                    try
                        if [Counter] = 0 
                            then [varDiff = listCumulative{[Counter]}, Counter = [Counter]+ 1]
                        else if listCategory{[Counter]} = listCategory{[Counter] - 1}
                            then [varDiff = listCumulative{[Counter]} - listCumulative{[Counter] -1}, Counter = [Counter]+ 1]
                            else [varDiff = listCumulative{[Counter]}, Counter = [Counter]+ 1]
                    otherwise [Counter = [Counter] + 1],
                each [varDiff]
            ),
            1
        ),
    CombinedColumns = 
        Table.ToColumns(#"Sorted Rows") & {listCumulativeDifference},
    BackToTable = 
        Table.FromColumns(
            CombinedColumns,
            Table.ColumnNames(#"Sorted Rows") & {"Difference"}
        )
in
    BackToTable

toAndFromCols LDS:

let
    Origine = LDS,
    decumul =(cumulist)=> 
    let
        ttc=Table.ToColumns(cumulist),
        names=Table.ColumnNames(cumulist),
        tfc = Table.FromColumns(ttc&{{0}&cumulist[CUMULATIVE VIEWS]},names&{"shifted"}),
        ac = Table.AddColumn(tfc, "dec", each [CUMULATIVE VIEWS]-[shifted]),
        rl = Table.RemoveLastN(ac,1)
    in
        rl,

    #"Raggruppate righe" = Table.Group(Origine, {"CATEGORY"}, {"all", each decumul(_)}),
    #"Tabella all espansa" = Table.ExpandTableColumn(#"Raggruppate righe", "all", {"DATETIME", "CUMULATIVE VIEWS", "HOURLY VIEWS (POWER QUERY CALCULATION)", "dec"}, {"DATETIME", "CUMULATIVE VIEWS", "HOURLY VIEWS (POWER QUERY CALCULATION)", "dec"})
in
    #"Tabella all espansa"

LDS:

let
    Origine = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("jZRBagMxDEWvEmYdiKWxR3Z2cY8RssgidFko3fT2HWtwodUXaGNIeBjP/9K73xdqF6ILJ2qnRFeSK/NyXt6eX6/3j8/v023/wdtxPM5/cXbwOg5Dr5heE6SzQ5f9KIYuSpOh235kQ2/47jz+WQ0tDi3wJRXTZd0Pm2DD9DYykf80JUzLoCkZ3GlTGAVOTplSUCjklCkwcHLKrDBwKg7dYChOmU1DMbRTZoNjRRWPFSWGT3HapAQz5OTcTmNWqsHJwRkOCzt9EsNPZadQWjd9kplcMFz9ICEOXqM4o5aQKpSGOSJVDFqjsisHVKF0hneD6epTWvZuMF1Kw41DqlC6RlXRp4ZaRBWDLgWNFjKF0hI1RZ/SCplC6Rw1hdISNcWgJUdN0afhQqYYdE1RUygtUVH06ayQJ5SuUU30XwmFNHHsMfxOpIljj+feP34A", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [DATETIME = _t, CATEGORY = _t, #"CUMULATIVE VIEWS" = _t, #"HOURLY VIEWS (POWER QUERY CALCULATION)" = _t]),
    mt= Table.TransformColumnTypes(Origine,{{"DATETIME", type datetime}, {"CATEGORY", type text}, {"CUMULATIVE VIEWS", Int64.Type}, {"HOURLY VIEWS (POWER QUERY CALCULATION)", Int64.Type}}),
    ttc=Table.ToColumns(mt),
    names=Table.ColumnNames(mt),
    largeDS= List.Transform(ttc, each List.Repeat(_,5000)),
    tfc=Table.FromColumns(largeDS,names)
in
    tfc