Code equivalent to Array Formula - arrays

Question

I am currently using an array formula in my data to find a row where columns O, Y, and AA match the current row, and where column A value does not match, and return column C for the matching row.
Here is my formula:
=INDEX(C:C,MATCH(1,(O:O=O2)*(Y:Y=Y2)*(AA:AA=AA2)*(A:A<>A2),0))
Using named ranges I have been able to input this formula using VBA, but what I really want to do is use VBA to perform a similar function and write the resulting value to column D.
I am thinking that possibly a loop, for each i from 2 to last row, find the other row within the range that matches and write cell(row that was found, 3).value to cell(i, 4), but I don't know the syntax for a VBA array to find that matching row.

Answer 1

While not explicitly stated, it could easily be inferred that you are seeking to use VBA to increase the efficiency of the calculation/recalculation of your array formula. You haven't provided the scope (i.e. number of rows) of your data but it is unlikely that you require the full column references you are using. The following calculation cycle times were based on ~1000 rows of static data.
Your array formula:
=INDEX(C:C, MATCH(1, (O:O=O2)*(Y:Y=Y2)*(AA:AA=AA2)*(A:A<>A2), 0))
Elapsed time to fill down and calculate: 24.828 seconds
Your array formula with column references truncated to actual extents of the data:
=INDEX($C$2:$C$999, MATCH(1, ($O$2:$O$999=O2)*($Y$2:$Y$999=Y2)*($AA$2:$AA$999=AA2)*($A$2:$A$999<>A2), 0))
Elapsed time to fill down and calculate: 0.203 seconds
Comparable standard formula with column references truncated to actual extents of the data:
=INDEX($C$2:$C$999, MIN(INDEX(ROW($1:$998)+(($A$2:$A$999=A2)+($O$2:$O$999<>O2)+($Y$2:$Y$999<>Y2)+($AA$2:$AA$999<>AA2))*1E+99, , )))
Elapsed time to fill down and calculate: 0.257 seconds
As you can see, cutting down the column references to what are actually being used increases efficiency immensely. Array formulas process by calculating everything against everything else. The calculation load increases exponentially
as the rows of cells referenced increases.
If your data is constantly changing and you do not know how many rows you will be dealing with, use named ranges with a Refers to: that is defined dynamically. Example:
Pick a column that usually defines the extents of the data and note the nature of the data. This method differs slightly depending upon whether you are dealing with true numbers or text. For demonstration purposes, column C has numbers.
Choose Formulas ► Defined Names► Name Manager. When the Name Manager dialog opens, click New.
Type a friendly name for the range in the Name: text box; e.g. MyColAA. Lave the Scope: as Workbook.
Use the following for the Refers to::     =$AA$2:INDEX($AA:$AA, MATCH(1e99, $C:$C)) 
This will define myColAA as AA2 to the row matching the last number in column C. If column C:C was full of text values you would use the following,     =$AA$2:INDEX($AA:$AA, MATCH("zzz", $C:$C)) 
Repeat for columns A:A, C:C, O:O and Y:Y. Keep the last used reference as column C:C so they will always have the same number of rows but change the other column references and give each a new name.
When you created all of the named ranges and are back at the worksheet, test one by tapping F5, typing myColAA into the Reference: text box and clicking OK.
Your array formula will now look similar to the following.
=INDEX(myColC, MATCH(1, (myColO=O2)*(myColY=Y2)*(myColAA=AA2)*(myColA<>A2), 0))
The named ranges will grow and shrink with the amount of data available.