I have a data frame of the following form:
Temp Depth Light x time date time.at.depth
104 18.59 -2.7 27 21:38 2012-06-20 4
109 18.59 -2.7 27 22:02 2012-06-20 5
110 18.75 -4.0 27 22:07 2012-06-20 5
113 18.91 -2.7 27 22:21 2012-06-20 4
114 18.91 -4.0 27 22:26 2012-06-20 5
115 18.91 -2.7 27 22:31 2012-06-20 5
117 18.91 -2.7 27 22:40 2012-06-20 4
118 18.75 -4.0 27 22:45 2012-06-20 5
119 18.75 -2.7 27 22:50 2012-06-20 5
121 18.59 -4.0 27 22:59 2012-06-20 4
122 18.75 -2.7 27 23:04 2012-06-20 5
123 18.75 -4.0 27 23:09 2012-06-20 5
126 18.59 -2.7 27 23:23 2012-06-20 5
127 18.59 -2.7 27 23:28 2012-06-20 5
128 18.59 -4.0 27 23:33 2012-06-20 5
133 18.75 -4.0 27 23:57 2012-06-20 5
136 18.59 -4.0 27 00:11 2012-06-20 5
138 18.59 -2.7 27 00:21 2012-06-20 5
140 18.91 -2.7 27 00:30 2012-06-20 5
I would like to subset the data into 30 minute bins. Is there an easy way to do this? I looked at the split() function but it appears that things need to be in a numeric format for that to work, I have time in POSIXct format. Any ideas would be greatly appreciated.
Here's a one-liner for you (dat being your dataframe):
split(dat, cut(strptime(paste(dat$date, dat$time), format="%F %R"),"30 mins"))
Indeed cut.POSIXt accepts as break values
an interval specification, one of "sec", "min", "hour", "day", "DSTday", "week", "month", "quarter" or "year", optionally preceded by an integer and a space, or followed by "s".
Additionnaly, I used %F %R as a shortcut for %Y-%m-%d %H:%M: see ?strptime to see all possible formats.
来源：https://stackoverflow.com/questions/15573468/split-or-subset-data-into-30-minute-intervals