Hi, I have a longitudianl data set with variables ID, days, outcome; Every ID has several measurement at different days. For example, one patient had vistis at day 1, 3, 7, 16, 20 and also outcome measurements on these days. Another patient had visits on day -2, 4, 6, 11, etc. I want to take out visits that is closest to day 0 and day 7, day 14, in the range of +-2 days, etc. and make data look like: ID, week, outcome 1, 0, 20 1, 1, 26 1, 2, 30 2, 0, 23 2, 1, NA 2, 2, 45 ... Currently I am using if-else statement and extract data at each time point into a separate data set and then merge those data sets. Any better solutions? Thanks.
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