Questions about doing analysis based on time

Thanks to everyone for their help so far.  It's been greatly appreciated.  I
have a new, but similar problem:

I have data that I have broken down by hour (median/mean for each hour).  I
would like to break it down further, by each half hour (0:00-0:29,
0:30-0:59, 1:00-1:29, 1:30-1:59, etc).  I thought cut.dates() from the chron
package would be able to do it, but I can't find anything in the chron
package documention.  I'm fairly certain that if I can figure out how to
break down the data by half hour that I can do all the other analysis just
fine (median/mean for each half hour, etc)


Here is a small sample of the data:

dput(head(SundayData, 100))

structure(list(SunDate = structure(c(1273377600, 1307851200,
1213502640, 1217736420, 1311480420, 1211688540, 1337487060, 1255839120,
1268543520, 1293945120, 1280635980, 1309061640, 1322975640, 1297574280,
1221970740, 1253420340, 1218946800, 1329024060, 1290316920, 1224994980,
1218342420, 1269750420, 1257658080, 1322371680, 1214108940, 1312086540,
1260077400, 1228023060, 1315110660, 1281241920, 1272774960, 1224995820,
1275194220, 1246768860, 1302410460, 1234071780, 1305434580, 1232257500,
1243140300, 1284871500, 1247373960, 1265521560, 1273985160, 1310273160,
1226209620, 1270356420, 1330235280, 1222577400, 1310878200, 1324187400,
1242535860, 1336279860, 1283057520, 1291528320, 1324187580, 1330840380,
1298786100, 1307854500, 1236491880, 1298786280, 1233468180, 1280034240,
1230444300, 1213506360, 1251608760, 1215320820, 1304226420, 1320556080,
1299391740, 1286687580, 1296972780, 1296972780, 1321164780, 1260684960,
1315113420, 1287292680, 1292134800, 1303017600, 1307251200, 1278825720,
1238304180, 1212902640, 1231655100, 1254029100, 1311485100, 1295159160,
1220160420, 1297578540, 1300599000, 1241933640, 1225604100, 1269149880,
1283665140, 1244958120, 1245562980, 1289716980, 1235890020, 1282456080,
1279432140, 1279432140), class = c("POSIXct", "POSIXt"), tzone = ""),
     SunTime = structure(c(1L, 1L, 2L, 3L, 3L, 4L, 5L, 6L, 6L,
     6L, 7L, 8L, 8L, 9L, 10L, 10L, 11L, 12L, 13L, 14L, 15L, 15L,
     16L, 16L, 17L, 17L, 18L, 19L, 19L, 20L, 21L, 22L, 22L, 23L,
     23L, 24L, 24L, 25L, 25L, 25L, 26L, 26L, 26L, 26L, 27L, 27L,
     28L, 29L, 29L, 29L, 30L, 30L, 31L, 31L, 32L, 32L, 33L, 33L,
     34L, 34L, 35L, 36L, 37L, 38L, 38L, 39L, 39L, 40L, 41L, 42L,
     42L, 42L, 42L, 43L, 44L, 45L, 46L, 46L, 46L, 47L, 48L, 49L,
     50L, 50L, 50L, 51L, 52L, 53L, 54L, 55L, 56L, 57L, 58L, 59L,
     60L, 60L, 61L, 62L, 63L, 63L), .Label = c("0:00", "0:04",
     "0:07", "0:09", "0:11", "0:12", "0:13", "0:14", "0:18", "0:19",
     "0:20", "0:21", "0:22", "0:23", "0:27", "0:28", "0:29", "0:30",
     "0:31", "0:32", "0:36", "0:37", "0:41", "0:43", "0:45", "0:46",
     "0:47", "0:48", "0:50", "0:51", "0:52", "0:53", "0:55", "0:58",
     "1:03", "1:04", "1:05", "1:06", "1:07", "1:08", "1:09", "1:13",
     "1:16", "1:17", "1:18", "1:20", "1:22", "1:23", "1:24", "1:25",
     "1:26", "1:27", "1:29", "1:30", "1:34", "1:35", "1:38", "1:39",
     "1:42", "1:43", "1:47", "1:48", "1:49", "1:52", "1:54", "1:55",
     "1:56", "1:57", "1:59", "10:00", "10:04", "10:07", "10:08",
     "10:09", "10:10", "10:11", "10:12", "10:14", "10:15", "10:16",
     "10:18", "10:20", "10:22", "10:23", "10:24", "10:25", "10:26",
     "10:27", "10:28", "10:30", "10:31", "10:32", "10:33", "10:34",
     "10:35", "10:36", "10:37", "10:38", "10:39", "10:40", "10:41",
     "10:43", "10:44", "10:45", "10:47", "10:48", "10:49", "10:50",
     "10:51", "10:53", "10:54", "10:55", "10:56", "10:58", "10:59",
     "11:01", "11:02", "11:05", "11:06", "11:07", "11:09", "11:10",
     "11:12", "11:14", "11:15", "11:16", "11:20", "11:21", "11:22",
     "11:23", "11:24", "11:26", "11:27", "11:29", "11:30", "11:31",
     "11:33", "11:34", "11:35", "11:36", "11:37", "11:38", "11:39",
     "11:40", "11:43", "11:44", "11:46", "11:47", "11:49", "11:52",
     "11:56", "11:58", "11:59", "12:00", "12:01", "12:02", "12:03",
     "12:04", "12:05", "12:06", "12:07", "12:08", "12:09", "12:10",
     "12:11", "12:13", "12:14", "12:15", "12:17", "12:19", "12:21",
     "12:22", "12:24", "12:25", "12:26", "12:27", "12:28", "12:30",
     "12:31", "12:32", "12:34", "12:36", "12:37", "12:38", "12:39",
     "12:41", "12:45", "12:46", "12:47", "12:48", "12:49", "12:50",
     "12:51", "12:53", "12:54", "12:55", "12:56", "12:57", "12:58",
     "12:59", "13:00", "13:01", "13:02", "13:03", "13:04", "13:05",
     "13:06", "13:07", "13:08", "13:09", "13:10", "13:12", "13:13",
     "13:14", "13:15", "13:17", "13:18", "13:19", "13:20", "13:21",
     "13:23", "13:25", "13:26", "13:27", "13:30", "13:31", "13:32",
     "13:34", "13:35", "13:36", "13:38", "13:39", "13:40", "13:44",
     "13:45", "13:46", "13:47", "13:48", "13:49", "13:50", "13:51",
     "13:52", "13:53", "13:54", "13:55", "13:57", "13:58", "13:59",
     "14:00", "14:01", "14:02", "14:04", "14:05", "14:06", "14:07",
     "14:08", "14:11", "14:12", "14:13", "14:14", "14:15", "14:16",
     "14:17", "14:18", "14:20", "14:21", "14:22", "14:23", "14:25",
     "14:26", "14:28", "14:29", "14:30", "14:31", "14:32", "14:34",
     "14:35", "14:36", "14:37", "14:38", "14:40", "14:41", "14:42",
     "14:43", "14:45", "14:46", "14:47", "14:49", "14:50", "14:51",
     "14:52", "14:53", "14:54", "14:56", "14:57", "14:58", "14:59",
     "15:01", "15:02", "15:03", "15:04", "15:05", "15:07", "15:11",
     "15:12", "15:13", "15:14", "15:15", "15:17", "15:18", "15:19",
     "15:20", "15:22", "15:23", "15:24", "15:25", "15:26", "15:28",
     "15:29", "15:30", "15:31", "15:33", "15:34", "15:35", "15:36",
     "15:37", "15:38", "15:40", "15:41", "15:42", "15:43", "15:44",
     "15:45", "15:46", "15:47", "15:48", "15:50", "15:51", "15:53",
     "15:54", "15:56", "15:57", "15:59", "16:01", "16:02", "16:04",
     "16:05", "16:06", "16:07", "16:09", "16:13", "16:14", "16:15",
     "16:16", "16:18", "16:19", "16:20", "16:21", "16:23", "16:24",
     "16:25", "16:26", "16:29", "16:30", "16:31", "16:32", "16:34",
     "16:35", "16:36", "16:37", "16:38", "16:40", "16:42", "16:43",
     "16:44", "16:45", "16:46", "16:47", "16:48", "16:49", "16:52",
     "16:55", "16:56", "16:57", "16:58", "16:59", "17:03", "17:04",
     "17:05", "17:06", "17:07", "17:11", "17:12", "17:13", "17:14",
     "17:15", "17:17", "17:18", "17:19", "17:20", "17:22", "17:24",
     "17:25", "17:27", "17:29", "17:32", "17:34", "17:35", "17:36",
     "17:37", "17:38", "17:40", "17:41", "17:45", "17:47", "17:49",
     "17:50", "17:52", "17:53", "17:55", "17:56", "17:57", "17:58",
     "17:59", "18:00", "18:01", "18:02", "18:04", "18:05", "18:06",
     "18:08", "18:09", "18:10", "18:11", "18:12", "18:13", "18:14",
     "18:16", "18:17", "18:18", "18:19", "18:20", "18:21", "18:22",
     "18:23", "18:24", "18:26", "18:27", "18:30", "18:31", "18:32",
     "18:33", "18:35", "18:36", "18:37", "18:38", "18:40", "18:41",
     "18:42", "18:43", "18:44", "18:49", "18:54", "18:55", "18:56",
     "18:58", "18:59", "19:00", "19:01", "19:02", "19:04", "19:05",
     "19:07", "19:08", "19:09", "19:10", "19:11", "19:12", "19:13",
     "19:14", "19:15", "19:16", "19:17", "19:18", "19:19", "19:20",
     "19:21", "19:22", "19:23", "19:24", "19:25", "19:26", "19:27",
     "19:28", "19:29", "19:30", "19:31", "19:32", "19:34", "19:35",
     "19:36", "19:37", "19:38", "19:40", "19:41", "19:42", "19:43",
     "19:44", "19:46", "19:47", "19:48", "19:49", "19:50", "19:51",
     "19:52", "19:53", "19:54", "19:55", "19:56", "19:57", "19:58",
     "2:01", "2:02", "2:07", "2:10", "2:11", "2:13", "2:14", "2:15",
     "2:16", "2:17", "2:18", "2:19", "2:20", "2:22", "2:23", "2:24",
     "2:25", "2:26", "2:28", "2:29", "2:31", "2:33", "2:34", "2:35",
     "2:38", "2:39", "2:42", "2:44", "2:45", "2:46", "2:51", "2:55",
     "2:56", "2:58", "2:59", "20:00", "20:02", "20:04", "20:07",
     "20:08", "20:10", "20:11", "20:12", "20:13", "20:14", "20:15",
     "20:17", "20:19", "20:20", "20:21", "20:22", "20:23", "20:24",
     "20:25", "20:27", "20:28", "20:29", "20:31", "20:32", "20:33",
     "20:34", "20:35", "20:38", "20:39", "20:40", "20:41", "20:42",
     "20:43", "20:45", "20:46", "20:49", "20:52", "20:53", "20:54",
     "20:55", "20:56", "20:57", "20:59", "21:00", "21:01", "21:02",
     "21:03", "21:04", "21:05", "21:07", "21:08", "21:09", "21:10",
     "21:12", "21:14", "21:15", "21:20", "21:21", "21:22", "21:23",
     "21:24", "21:25", "21:26", "21:27", "21:28", "21:30", "21:31",
     "21:32", "21:34", "21:36", "21:37", "21:38", "21:39", "21:42",
     "21:45", "21:46", "21:48", "21:49", "21:50", "21:51", "21:53",
     "21:54", "21:55", "21:56", "21:57", "21:58", "21:59", "22:01",
     "22:02", "22:04", "22:05", "22:06", "22:08", "22:09", "22:10",
     "22:11", "22:12", "22:13", "22:14", "22:16", "22:17", "22:18",
     "22:19", "22:21", "22:22", "22:23", "22:24", "22:25", "22:26",
     "22:27", "22:28", "22:29", "22:30", "22:31", "22:32", "22:34",
     "22:35", "22:36", "22:37", "22:39", "22:40", "22:41", "22:42",
     "22:45", "22:48", "22:49", "22:53", "22:54", "22:56", "22:59",
     "23:00", "23:01", "23:02", "23:04", "23:05", "23:06", "23:08",
     "23:09", "23:10", "23:11", "23:14", "23:15", "23:17", "23:18",
     "23:19", "23:21", "23:22", "23:26", "23:27", "23:28", "23:30",
     "23:32", "23:33", "23:34", "23:36", "23:37", "23:38", "23:40",
     "23:41", "23:42", "23:43", "23:44", "23:45", "23:46", "23:47",
     "23:48", "23:49", "23:50", "23:52", "23:53", "23:54", "23:55",
     "23:58", "23:59", "3:02", "3:04", "3:05", "3:06", "3:07",
     "3:10", "3:11", "3:12", "3:15", "3:19", "3:20", "3:22", "3:24",
     "3:25", "3:27", "3:28", "3:30", "3:31", "3:32", "3:33", "3:34",
     "3:35", "3:36", "3:39", "3:43", "3:44", "3:45", "3:50", "3:51",
     "3:52", "3:53", "3:55", "3:56", "3:57", "3:58", "3:59", "4:00",
     "4:01", "4:02", "4:06", "4:07", "4:09", "4:16", "4:21", "4:26",
     "4:28", "4:29", "4:31", "4:32", "4:36", "4:37", "4:39", "4:40",
     "4:44", "4:46", "4:47", "4:52", "4:53", "4:54", "4:56", "4:57",
     "4:59", "5:03", "5:05", "5:06", "5:08", "5:14", "5:16", "5:17",
     "5:18", "5:19", "5:21", "5:23", "5:27", "5:29", "5:30", "5:32",
     "5:34", "5:36", "5:37", "5:38", "5:39", "5:40", "5:42", "5:43",
     "5:45", "5:46", "5:47", "5:48", "5:50", "5:52", "5:54", "5:56",
     "5:59", "6:00", "6:01", "6:06", "6:07", "6:08", "6:10", "6:11",
     "6:14", "6:15", "6:16", "6:17", "6:19", "6:20", "6:22", "6:24",
     "6:25", "6:27", "6:29", "6:30", "6:31", "6:32", "6:33", "6:35",
     "6:39", "6:40", "6:42", "6:43", "6:44", "6:46", "6:47", "6:48",
     "6:49", "6:50", "6:52", "6:54", "6:56", "6:57", "6:58", "6:59",
     "7:00", "7:02", "7:03", "7:04", "7:06", "7:08", "7:09", "7:13",
     "7:18", "7:20", "7:23", "7:25", "7:26", "7:28", "7:29", "7:33",
     "7:34", "7:35", "7:36", "7:38", "7:39", "7:40", "7:41", "7:43",
     "7:44", "7:45", "7:46", "7:49", "7:50", "7:52", "7:53", "7:54",
     "7:55", "7:56", "7:58", "7:59", "8:01", "8:02", "8:04", "8:05",
     "8:08", "8:11", "8:12", "8:13", "8:16", "8:19", "8:21", "8:24",
     "8:25", "8:28", "8:29", "8:30", "8:31", "8:34", "8:35", "8:36",
     "8:38", "8:39", "8:40", "8:41", "8:43", "8:45", "8:47", "8:48",
     "8:49", "8:50", "8:51", "8:52", "8:53", "9:00", "9:02", "9:03",
     "9:04", "9:06", "9:07", "9:08", "9:10", "9:13", "9:15", "9:16",
     "9:19", "9:20", "9:22", "9:24", "9:25", "9:26", "9:28", "9:29",
     "9:33", "9:34", "9:35", "9:36", "9:37", "9:40", "9:41", "9:42",
     "9:45", "9:46", "9:47", "9:48", "9:54", "9:56", "9:58", "9:59"
     ), class = "factor"), SunScore = c(127L, 125L, 98L, 118L,
     122L, 104L, 124L, 121L, 117L, 131L, 142L, 102L, 136L, 200L,
     88L, 142L, 84L, 23L, 103L, 167L, 116L, 168L, 151L, 105L,
     95L, 180L, 55L, 105L, 144L, 155L, 174L, 141L, 153L, 130L,
     112L, 116L, 147L, 143L, 165L, 183L, 161L, 140L, 134L, 113L,
     151L, 138L, 200L, 116L, 146L, 200L, 152L, 151L, 117L, 156L,
     82L, 68L, 200L, 129L, 81L, 114L, 144L, 110L, 132L, 53L, 42L,
     117L, 65L, 127L, 106L, 129L, 159L, 159L, 110L, 120L, 114L,
     129L, 54L, 81L, 154L, 139L, 132L, 69L, 32L, 60L, 74L, 82L,
     135L, 161L, 106L, 114L, 71L, 60L, 120L, 81L, 121L, 59L, 130L,
     128L, 200L, 155L)), .Names = c("SunDate", "SunTime", "SunScore"
), row.names = c(NA, 100L), class = "data.frame")

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