Excel Advice 440K rows

I need to create a VBA script that will scan the current xls sheet (XLSA) (one column in up to for sheets) and compare it to a second xls (XLSB) to check if the ID has bee used before. Easy enough, except that the xls being compared to has 443K rows.

Just wanting advice to best tackle this. Should I read the entire 440K rows (a single column) into an array then scan the array for the value in XLSA on each row? or use Find? it needs to be very accurate in that we cannot have a duplicate ID.

Thanks!

I would first sort the 443K ID column in ascending order and use a binary search algorithm to search the for the test value. This will help no matter which memory usage scheme you select by minimizing value look up and comparisons. I found this comparison of Find vs Binary search that you can review. http://stackoverflow.com/a/1893241/2592875

You can implement the search on either the sorted column or read the values into an array. If the values are strictly numeric (Integer) or comprise relatively short strings, I would tend to use an array. If they are long strings, you will have to evaluate the impact of consuming a large amount of memory versus the cost of directly accessing the Worksheet.

its not big... xls file is like 4 mb so the text will be less.... I wonder If I can push the compare list out as a CSV to make it smaller before even loading.

Thanks!

i am reasonable sure a collection would work faster than an array for lookups, even though you would have to process all the values into the collection first, there was a thread about this in the vb6 forum about a couple of months ago

Static,

Do you need to confirm whether or not there are already duplicates in the list of 443k, or just that the new value (in sheet A) is not already in the big list?

It sounds like you're just wanting to vlookup the values to test for duplicates. If they're all #N/A then they are unique. A lookup on 440k rows with a low hit-rate could take a long time. You could try this addin that works using a background SQLite database for indexed matching:

http://fastervlookup.codeplex.com/