在R中减去超过24小时的时间数据

Question

My data consists of time points, in hours, starting from the start point of the experiment. Experiments usually take over a week, so the the amount of hours easily exceeds 24.

To be precise, data is in the following format: 162:43:33.281 hhh:mm:ss.msecs at the start of the experiment data points could consist of just 1-2 values for the hour insetad of the 3 mentioned here.

When I try to substract 2 times points I get an error stating that the numerical expression has for exemple 162:43 elements, which obviously refers to the colon used in the time annotation.

Any ideas on how to be able to treat time variables that consist of hour values over 24? I tried the strptime function, with %H as argument, but that limits me to 24 hours.

Here is some example data:

V1           V2 V3        V4                       V5             
75:45:32.487 NA 17       ####revFalsePoke is 112  TRUE
75:45:32.487 NA 17          ####totalwindow is 5  TRUE
75:46:32.713 NA  1          ####Criteria not met  TRUE
75:46:49.846 NA  6      ####revCorrectPoke is 37  TRUE
75:46:52.336 NA  9   ####revDeliberateLick is 34  TRUE
75:46:52.351 NA  9          ####totalwindow is 5  TRUE
75:46:52.598 NA  1          ####Criteria not met  TRUE
75:47:21.332 NA  6      ####revCorrectPoke is 38  TRUE
75:47:23.440 NA  9   ####revDeliberateLick is 35  TRUE
75:47:23.455 NA  9          ####totalwindow is 6  TRUE
75:47:23.657 NA  1      ####rev Criteria not met  TRUE
75:47:44.731 NA 17       ####revFalsePoke is 113  TRUE
75:47:44.731 NA 17          ####totalwindow is 6  TRUE

Answer 1

Unfortunately, you're going to have to roll your own converter function for this. I suggest converting the timestamps to difftime objects (which represent time duration, rather than location). You can then add them to some starting datetime to arrive at a final datetime for each timestamp. Here's one approach:

f <- function(start, timestep) {
    result <- mapply(function(part, units) as.difftime(as.numeric(part), units=units), 
                     unlist(strsplit(timestep, ':')), 
                     c('hours', 'mins', 'secs'),
                     SIMPLIFY=FALSE)
    start + do.call(sum, result)
}

start <- as.POSIXct('2013-1-1')
timesteps <- c('162:43:33.281', '172:34:28.33')
lapply(timesteps, f, start=start)
# [[1]]
# [1] "2013-01-07 18:43:33.280 EST"
# 
# [[2]]
# [1] "2013-01-08 04:34:28.32 EST"