Excel or Power Query: Merge/Lookup Closest Previous Date

Question

everyone:

I have a table with these dates:

I have another table with a list of dates and owners:

I need to merge/join these two tables so that the transaction dates are matched up with the closest previous start date so that it looks like this:

I tried using XLOOKUP with "-1" but that was a problem because XLOOKUP retrieved the first record for transaction date 4/16/2017 (which has 2 matches) and I couldn't merge on Power Query since there are no exact date matches. Is there another way?

Thank you.

Answer 1

Assuming this table is named Table4, you first need to group because of your duplicate dates for e and f.

let
    Source = Excel.CurrentWorkbook(){[Name="Table4"]}[Content],
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Start Date", type text}, {"Owner", type text}}),
    #"Changed Type with Locale" = Table.TransformColumnTypes(#"Changed Type", {{"Start Date", type date}}, "en-US"),
    #"Grouped Rows" = Table.Group(#"Changed Type with Locale", {"Start Date"}, {{"All", each _, type table [Start Date=nullable date, Owner=nullable text]}})
in
    #"Grouped Rows"

Assuming this table is named Table3, you can then add a custom column as described here

The code for this table is

let
    Source = Excel.CurrentWorkbook(){[Name="Table3"]}[Content],
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Transaction Dates", type text}}),
    #"Changed Type with Locale" = Table.TransformColumnTypes(#"Changed Type", {{"Transaction Dates", type date}}, "en-US"),
    #"Added Custom" = Table.AddColumn(#"Changed Type with Locale", "Custom", (i) => Table.Last( Table.Sort( Table.SelectRows(Table4,each [Start Date] <= i[Transaction Dates]),{"Start Date", Order.Ascending}))),
    #"Expanded Custom" = Table.ExpandRecordColumn(#"Added Custom", "Custom", {"Start Date", "All"}, {"Custom.Start Date", "Custom.All"}),
    #"Expanded Custom.All" = Table.ExpandTableColumn(#"Expanded Custom", "Custom.All", {"Owner"}, {"Owner"})
in
    #"Expanded Custom.All"