Subtract two rows based on condition

[Anonymous]

Hello, 

I am trying to subtract two consecutive rows from each other (Power) based on a condition from another column (Day No.) to yield a new value (Power_2) as shown below. However, once a new Day No. is reached, the first value of that day will remain the same and be copied into the Power_2 column. 

Thanks

[Mariusz · Accepted solution]

Hi @Anonymous 

Hope this works for you.

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("RcqxDcAwDAPBXVirsKjYyxjaf40EQoDvrrh7lQrlUsfPhIY1NNfc4YZnWB+9YELDgo+6Xw==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [Day = _t, Power = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Day", Int64.Type}, {"Power", Int64.Type}}),
    #"Added Custom" = Table.AddColumn(#"Changed Type", "Power_2", each let _day = [Day], _power = [Power] 
        in [Power] - Replacer.ReplaceValue( List.Max( Table.SelectRows( #"Changed Type", each [Day] = _day and  [Power] < _power )[Power]), null, 0 ), Int64.Type )
in
    #"Added Custom"

Best Regards,
Mariusz

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