Hi everyone, I'm dealing with a longitudinal dataset with about 10-year follow-up. Each subject has a unique ID, dates of clinic visits, test results. Each subject had multiple clinic visits (different dates).The data looks as: ID Date Result 001 Jan01/10 Pos 001 Mar28/12 Pos 001 Jan30/13 Neg 001 May04/12 Pos 001 Jun20/10 Neg 002 Jan01/10 Neg 002 Mar28/12 Neg 002 Feb30/13 Neg 002 May04/12 Neg 002 Jun20/10 Neg 003 Oct01/14 Neg 003 Mar28/12 Pos 003 Jan30/14 Neg 004 May04/12 Pos 005 Jun29/16 Neg ..... I am trying to select observations across their entire follow-up time with evenly distributed length of time. i.e. if a subject has a 5-year follow-up with multiple visits, I'd like to select the most evenly distributed observations across the 5 years. Let's say I need select 3 time points, ideally it'd be the the first date, the last date (first and last dates are required), and the 2.5(half of 5-year) date (or any dates close to the 2.5 point). I'm able to filter the first and last dates by using if first. / if last. statements, but having problems with the time points in between. Thanks all ahead
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