I have a dataset like this (dput for this below) which represents user computer sessions:
username machine start end 1 user1 D5599.domain.com 2011-01-03 09:44:18 2011-01-03 09:47:27 2 user1 D5599.domain.com 2011-01-03 09:46:29 2011-01-03 10:09:16 3 user1 D5599.domain.com 2011-01-03 14:07:36 2011-01-03 14:56:17 4 user1 D5599.domain.com 2011-01-05 15:03:17 2011-01-05 15:23:15 5 user1 D5599.domain.com 2011-02-14 14:33:39 2011-02-14 14:40:16 6 user1 D5599.domain.com 2011-02-23 13:54:30 2011-02-23 13:58:23 7 user1 D5599.domain.com 2011-03-21 10:10:18 2011-03-21 10:32:22 8 user1 D5645.domain.com 2011-06-09 10:12:41 2011-06-09 10:58:59 9 user1 D5682.domain.com 2011-01-03 12:03:45 2011-01-03 12:29:43 10 USER2 D5682.domain.com 2011-01-12 14:26:05 2011-01-12 14:32:53 11 USER2 D5682.domain.com 2011-01-17 15:06:19 2011-01-17 15:44:22 12 USER2 D5682.domain.com 2011-01-18 15:07:30 2011-01-18 15:42:43 13 USER2 D5682.domain.com 2011-01-25 15:20:55 2011-01-25 15:24:38 14 USER2 D5682.domain.com 2011-02-14 15:03:00 2011-02-14 15:07:43 15 USER2 D5682.domain.com 2011-02-14 14:59:23 2011-02-14 15:14:47 > There may be serveral concurrent sessions for same username from the same computer. How can I remove those rows so that only one sessions is left for this data? I have no idea how to do this, maybe using difftime? -J structure(list(username = c("user1", "user1", "user1", "user1", "user1", "user1", "user1", "user1", "user1", "USER2", "USER2", "USER2", "USER2", "USER2", "USER2" ), machine = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 2L, 3L, 3L, 3L, 3L, 3L, 3L, 3L), .Label = c("D5599.domain.com", "D5645.domain.com", "D5682.domain.com", "D5686.domain.com", "D5694.domain.com", "D5696.domain.com", "D5772.domain.com", "D5772.domain.com", "D5847.domain.com", "D5855.domain.com", "D5871.domain.com", "D5927.domain.com", "D5927.domain.com", "D5952.domain.com", "D5993.domain.com", "D6012.domain.com", "D6048.domain.com", "D6077.domain.com", "D5688.domain.com", "D5815.domain.com", "D6106.domain.com", "D6128.domain.com" ), class = "factor"), start = structure(c(1294040658, 1294040789, 1294056456, 1294232597, 1297686819, 1298462070, 1300695018, 1307603561, 1294049025, 1294835165, 1295269579, 1295356050, 1295961655, 1297688580, 1297688363), class = c("POSIXct", "POSIXt"), tzone = ""), end = structure(c(1294040847, 1294042156, 1294059377, 1294233795, 1297687216, 1298462303, 1300696342, 1307606339, 1294050583, 1294835573, 1295271862, 1295358163, 1295961878, 1297688863, 1297689287), class = c("POSIXct", "POSIXt"), tzone = "")), .Names = c("username", "machine", "start", "end"), row.names = c(NA, 15L), class = "data.frame") ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.