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Asked: 2026-06-15T12:34:07+00:00

I’m reading in a CSV into a variable stuff and coercing the first column

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I’m reading in a CSV into a variable “stuff” and coercing the first column to POSIXct (this column only has timestamps, of the form “2012-12-04 17:49:52”, so this works well). 

stuff[,1]<-as.POSIXct(stuff[,1])

Since I have several days’ worth of data, I’m then trying to break things up by date:

control <- subset(stuff,as.Date(stuff[,1]) == '2012-11-27')
control.1 <- subset(stuff,as.Date(stuff[,1]) == '2012-11-28')

I find that this doesn’t split the data up by dates as I would expect.
tail(control) shows me that the last value is at 2012-11-27 15:54:21, while head(control.1) shows that its first value is 2012-11-27 16:04:35.

The equality therefore seems to pivot somewhere around 16:00 for some reason. I tried specifying timezones when coercing to POSIXct, but this didn’t help either. Is there anything I can do to subset by day (and is there a reason this failed)? I’d like to mention that I need to keep the hourly information in there, since I plan on using it to slice up the data subsequently.

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1 Answer

  1. Editorial Team

    Perhaps cut might be of use to you, but it is hard to tell for sure without a sample of your data that replicates the problem you’re having.

    Here’s a minimal example of using cut to create your daily subsets.

    set.seed(1) # So you can get the same numbers as I do
MyDates <- ISOdatetime(2012, 1, 1, 0, 0, 0, tz = "GMT") + sample(1:500000, 100)
class(MyDates)
# [1] "POSIXct" "POSIXt" 
split(MyDates, cut(MyDates, breaks="1 day"))
$`2012-01-01`
 [1] "2012-01-01 08:34:53 GMT" "2012-01-01 17:26:15 GMT" "2012-01-01 01:51:35 GMT"
 [4] "2012-01-01 14:59:28 GMT" "2012-01-01 03:14:25 GMT" "2012-01-01 09:48:56 GMT"
 [7] "2012-01-01 13:48:48 GMT" "2012-01-01 11:41:58 GMT" "2012-01-01 16:53:56 GMT"
[10] "2012-01-01 19:54:00 GMT" "2012-01-01 08:11:02 GMT"

$`2012-01-02`
 [1] "2012-01-02 12:52:35 GMT" "2012-01-02 04:00:41 GMT" "2012-01-02 04:36:26 GMT"
 [4] "2012-01-02 00:31:17 GMT" "2012-01-02 05:27:47 GMT" "2012-01-02 13:06:44 GMT"
 [7] "2012-01-02 23:16:05 GMT" "2012-01-02 01:51:43 GMT" "2012-01-02 09:59:46 GMT"
::::
::::
::::
[13] "2012-01-05 10:25:04 GMT" "2012-01-05 20:34:21 GMT" "2012-01-05 11:56:40 GMT"
[16] "2012-01-05 02:56:40 GMT" "2012-01-05 09:08:00 GMT" "2012-01-05 02:45:00 GMT"
[19] "2012-01-05 12:09:45 GMT" "2012-01-05 14:42:59 GMT" "2012-01-05 16:35:56 GMT"

$`2012-01-06`
 [1] "2012-01-06 06:08:22 GMT" "2012-01-06 04:46:31 GMT" "2012-01-06 11:12:12 GMT"
 [4] "2012-01-06 17:45:37 GMT" "2012-01-06 09:48:54 GMT" "2012-01-06 00:47:02 GMT"
 [7] "2012-01-06 06:46:24 GMT" "2012-01-06 01:33:21 GMT" "2012-01-06 03:53:53 GMT"
[10] "2012-01-06 00:01:45 GMT" "2012-01-06 13:23:54 GMT" "2012-01-06 01:40:54 GMT"
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