Countif across workbooks

[vivekmartin]

Hi,

I have a project with 2 million rows of data (13 digit numbers, single column). I need a method to find duplicates among this population. But I'm not sure how to run a countif function because Excel 2013 limits rows to a little over 1 million and hence my data is in two workbooks to maintain some sanity. I did search the forum for a similar problem, but failed to find one. Please be kind.