difference between two rows in the power query (m-language)

Hi William_Moreno 

Here is another method.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjIwMtQ1MNc1MFTSUXJKLcrJzAUyDA0MjExNwQw9U6VYHTR1Qfm5qSiqDLGp8kstV4jML8pGUWmEotICp73GegaY6jDsxWIWVlstlGJjAQ==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [date = _t, unit = _t, sku = _t, value = _t]),
    #"Changed Type with Locale" = Table.TransformColumnTypes(Source, {{"date", type date}, {"value", type number}}, "en-US"),
    #"Added Index" = Table.AddIndexColumn(#"Changed Type with Locale", "Index", 0, 1, Int64.Type),
    #"Grouped Rows" = Table.Group(#"Added Index", {"unit", "sku"}, {{"Groups", each _, type table [date=nullable text, unit=nullable text, sku=nullable text, value=nullable number]}}),
    #"Added Custom" = Table.AddColumn(#"Grouped Rows", "Groups2", each Table.AddIndexColumn([Groups], "sort", 0, 1, Int64.Type)),
    #"Removed Other Columns" = Table.SelectColumns(#"Added Custom",{"Groups2"}),
    #"Expanded GroupsIndex" = Table.ExpandTableColumn(#"Removed Other Columns", "Groups2", {"date", "unit", "sku", "value", "Index", "sort"}, {"date", "unit", "sku", "value", "Index", "sort"}),
    #"Added Custom1" = Table.AddColumn(#"Expanded GroupsIndex", "Difference", each if [sort] = 0 then 0 else [value] - Table.SelectRows(#"Expanded GroupsIndex", (x)=> x[unit]=[unit] and x[sku]=[sku] and x[sort]=[sort]-1){0}[value]),
    #"Sorted Rows" = Table.Sort(#"Added Custom1",{{"Index", Order.Ascending}}),
    #"Removed Columns" = Table.RemoveColumns(#"Sorted Rows",{"Index", "sort"})
in
    #"Removed Columns"

Regards,
Community Support Team _ Jing
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