Power Query append ,removing duplicate rows

Hello Anonymous 

what you can do is to take the older file, join it with the newer file using a LeftAnti-join (IDs from the newer file will be removed) and then combining with the newer file. If you have a lot of files this could be some challengen. Another option could be to integrate the creation date of the file or another information that gives you somehow a information of time and then group by id, then taking only the date with max value. Here an example on what I mean

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMlTSUXJJTU7NTUotUjAy0AFiIwMUMUO4mIqJAYgC8gz1DUBIKVYnWskIRbURFhMQYiqm2EwwxqFaAYrRlJsAhfyTS/LBquGKYSImCMsMDUixDSGGZIQxignGCAf45ZdBVCOCBy5ESL8psmJjhH5/qJAprvCC6jdD1m+Jab8hUpSZYRgQCwA=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [ID = _t, #"Application Received Date" = _t, #"Application Assessed Date" = _t, #"Funding Amount" = _t, #"Creation date" = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"ID", Int64.Type}, {"Application Received Date", type date}, {"Application Assessed Date", type date}, {"Funding Amount", type text}, {"Creation date", type date}}),
    #"Grouped Rows" = Table.Group(#"Changed Type", {"ID"}, {{"MaxCreationDate", each Table.Max(_,"Creation date")}}),
    #"Expanded MaxCreationDate" = Table.ExpandRecordColumn(#"Grouped Rows", "MaxCreationDate", {"Application Received Date", "Application Assessed Date", "Funding Amount", "Creation date"}, {"Application Received Date", "Application Assessed Date", "Funding Amount", "Creation date"})
in
    #"Expanded MaxCreationDate"

transforms this

into this

Copy paste this code to the advanced editor in a new blank query to see how the solution works.

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Have fun

Jimmy