In reference to the above question, I apologize but I've posed the question incorrectly. Let me try again.
I have two lists consisting of dates and measurements. I would like to deduplicate the first list by eliminating elements that (partially) match elements in the second.
Here is the first list:
lis1 = {{Today, "a", 2, "b", 2}, {Today, "c", 3, "d", 3}, {Today, "e", 5, "f", 6}, {Today, "g", 7, "h", 8}};
The second list is structured similarly, with the exception that the Date may be any of the 3 days prior to today, say:
lis2 = {{DatePlus[Today,-2],"a","xx","b","xx"},{DatePlus[Today,-1],"e","xx","f","xx"}, {DatePlus[Today,-3],"p","xx","q","xx"}}
I'd like to strike the members of lis1 where the second (a, e) and fourth (b, f) sub-elements of the list members are identical to the second and fourth sub-elements of some member of lis2, resulting in:
res = {{Today, "c", 3, "d", 3},{Today, "g", 7, "h", 8}}
Hope this is clearer!