Need to distinguish between first and second data occurence

[bellows18]

I have time and date data that uniquely corresponds to a location ID. The data I received is in 12 hour format without any indicators of AM or PM. Each of these unique time and dates has a duplicate meaning one is AM and one is PM.

Is there an if statement that can be written to output a 1 for the first occurrence of that time and date and a 2 for the second occurrence?

Thanks!

[Sam Capricci]

maybe =COUNTIF($A$2:A2,A2) and dragged down?

[bellows18]

That was just outputting a "2" for all occurrences unfortunately

[Sam Capricci]

Without seeing what the data looks like it is difficult to develop a good formula. Go advanced to upload a small sample so you can get better help.

[bellows18]

To clarify, I have about 90,000 cells of data (90,000 rows.) Each has a date and time in the same cell and they are all formatted the same. What I'm looking for is for the formula to search the cells and output a 1 for the first occurrence of the specific date and time and a 2 for the second occurrence.

For example, 2015/09/01-01:00 is cell E2 and 2015/09/01-01:00 is cell E14543. In column F, I would like an output of 1 in F2 and output of 2 in F14543. Does that make sense?