Conditionally deleting repeated observations

[zfusfeld]

Hello all,

I have a somewhat complex conditional delete that I am trying to figure out, and it is based on repeated observations, and I have three different types of repeaters that need to be pruned. Essentially, I have a dataset with people who have been interviewed at 2 times. 

I want to delete observations for all of these repeaters so that they only have one visit in the dataset, and I would like to do this conditionally on two variables (ACECAT, which is ACEs category, and INT_D, which is interview date). There are three types of repeaters that I need to remove one visit from. They can be identified as repeaters via the use of another variable, site_ID (though in this dataset I've actually restricted so that only repeaters are present).

The first type of repeater is missing ACECAT at BOTH visits - for these, it doesn't really matter which observation gets deleted, but for the sake of consistency I would like to delete the first observation and keep the last. INT_D is formatted in DDMMMYYYY format. 

the second type of repeater has answered ACECAT at one visit and is missing ACECAT in the other visit - for these types of repeaters, I want to drop the observation where ACECAT is missing. 

the third type of repeater has answered ACECAT at both visits. For these types of repeaters, I want to keep only the most recent observation and drop the last observation. 

I've been trying to think of a data step (or multiple data steps if needed) that can solve this problem, but am drawing a blank. Can anyone help?

[maguiremq]

Can you provide us with some example data so that we can test out code? Thanks.

[mkeintz]

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@zfusfeld wrote:

the third type of repeater has answered ACECAT at both visits. For these types of repeaters, I want to keep only the most recent observation and drop the last observation. 

If your data are sorted by INT_D within each id/group, then isn't the most recent observation (to be kept) the same as the last observation (to be dropped)?