Subset data set by removing records with only one row per hour

[Buck1480]

I have a data set of GPS locations for a wildlife research project. GPS locations were collected 2x per hour (every 30 mins). However, the GPS collars sometimes would miss a location resulting in 1 location/hour. I need to subset my data set to only include locations where I have 2 GPS locations per hour (i.e., remove rows with only one location per hour). My issue is that due to the hierarchical data structure (GPS locations are nested within individual animal ID, Month, Day, Year, and Hour) I cannot find a simple solution to remove rows with only 1 location/hour. In the example data set below, I would only keep the locations at 10 am and 10:30 am (noted in red). In other words, I need to obtain a final file that contains only data with 2 locations per hour. Thanks for any help that you can provide!

Collar_ID	DATETIME	WEEK	YEAR	MONTH	DAY	HOUR	MOVEMENT_DISTANCE	NET_DISPLACEMENT
33827	10/1/2013 8:00	1	1	10	1	8	10	3.6
33827	10/1/2013 10:00	1	1	10	1	10	78.1	135.4
33827	10/1/2013 10:30	1	1	10	1	10	99.8	205.7
33827	10/1/2013 11:00	1	1	10	1	11	92.7	222.7
33827	10/1/2013 13:00	1	1	10	1	13	27.7	370.5
33827	10/1/2013 14:30	1	1	10	1	14	8	372.0
33827	10/1/2013 15:00	1	1	10	1	15	5	366.0

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[Rick Rothstein]

Why wouldn't the last two (which are within 1/2 hour of each other) be retained? Is it because the first one does not start "on the hour"?

 

[Buck1480]

Why wouldn't the last two (which are within 1/2 hour of each other) be retained? Is it because the first one does not start "on the hour"?

That's correct! First location needs to be at the start of the hour (e.g., 14:00 followed by the second location at 14:30).