special vlookup in power query - powerquery

Question

thank you for answering our questions. Look at the picture below. Transfer the rate value appropriately from the first to the second range.

Answer 1

If I understand you correctly, the code below should do what you require.
Read the code comments and explore the Applied Steps to better understand the algorithm.
let
//Read in the lookup table
Source = Excel.CurrentWorkbook(){[Name="Table1"]}[Content],
lookupTable = Table.TransformColumnTypes(Source,{
{"Date", Int64.Type},
{"P Code",Int64.Type},
{"SRC", Int64.Type},
{"Rate", Int64.Type}
}),
//read in data table
Source2 = Excel.CurrentWorkbook(){[Name="Table2"]}[Content],
typeIt2 = Table.TransformColumnTypes(Source2,{
{"Date", Int64.Type},
{"P.Code", Int64.Type},
{"Src", Int64.Type}
}),
//Join the two tables based on PCode and Src
join = Table.NestedJoin(typeIt2,{"P.Code","Src"},lookupTable,{"P Code","SRC"},"Joined", JoinKind.LeftOuter),
//for each joined subtable
// Sort descending by date
// Select only those rows where the date in table 2 is >= the corresponding date from table 1
// Then extract the first row Rate value (as that will be the closest to the date in table 2)
#"Added Custom" = Table.AddColumn(join, "Rate", each Table.SelectRows(Table.Sort([Joined],
{"Date",Order.Descending}),(t)=> t[Date] <= [Date])[Rate]{0}, Int64.Type),
//Remove unneeded join table column
#"Removed Columns" = Table.RemoveColumns(#"Added Custom",{"Joined"})
in
#"Removed Columns"
Lookup Table
Results