[R] Re sults sometimes in seconds with difftime unit=mins

Fri Mar 27 16:55:44 CET 2009

I think the problem is is that 'diff' does not have a 'units'
parameter; 'difftime' does.  Here is a way of doing it:

> x
 [1] "2009-03-27 13:00:00 EDT" "2009-03-27 13:00:35 EDT" "2009-03-27
13:01:10 EDT" "2009-03-27 13:01:45 EDT" "2009-03-27 13:02:20 EDT"
"2009-03-27 13:02:55 EDT" "2009-03-27 13:03:30 EDT"
 [8] "2009-03-27 13:04:05 EDT" "2009-03-27 13:04:40 EDT" "2009-03-27
13:05:15 EDT"
> difftime(tail(x, -1), head(x, -1), units='mins')
Time differences in mins
[1] 0.5833333 0.5833333 0.5833333 0.5833333 0.5833333 0.5833333
0.5833333 0.5833333 0.5833333
attr(,"tzone")
[1] ""
> diff(x, units='mins')  # 'units' ignored
Time differences in secs
[1] 35 35 35 35 35 35 35 35 35
attr(,"tzone")
[1] ""
>

On Fri, Mar 27, 2009 at 11:04 AM, Ptit_Bleu <ptit_bleu at yahoo.fr> wrote:
>
> Hello,
>
> I'm trying to calculate an integration and x-axis is a time (format :
> %Y-%m-%d %H:%M:%S").
> I use diff(date, units="mins") in a loop for but sometimes the results stay
> in seconds (95% is ok).
>
> Examples for 2 sets of data are given below (first result stays in seconds
> whereas the second in minutes as expected).
> Have you already seen this behaviour ?
> Any idea to solve this problem ?
>
> Thanks in advance.
> Have a good week-end,
> Ptit Bleu.
>
> ------------------------------------------------------------------------
>> strptime(datajour$Date, format="%Y-%m-%d %H:%M:%S")
>  [1] "2009-03-26 11:21:31" "2009-03-26 11:22:17" "2009-03-26 11:27:18"
> "2009-03-26 11:36:59" "2009-03-26 11:41:59" "2009-03-26 11:46:59"
>  [7] "2009-03-26 11:51:59" "2009-03-26 11:57:00" "2009-03-26 12:02:00"
> "2009-03-26 12:07:00" "2009-03-26 12:12:00" "2009-03-26 12:17:00"
> [13] "2009-03-26 12:22:00" "2009-03-26 12:27:01" "2009-03-26 12:32:01"
> "2009-03-26 12:37:01" "2009-03-26 12:42:01" "2009-03-26 12:47:01"
> [19] "2009-03-26 12:52:01" "2009-03-26 12:57:01" "2009-03-26 13:02:02"
> "2009-03-26 13:07:02" "2009-03-26 13:12:03" "2009-03-26 13:17:03"
> [25] "2009-03-26 13:22:03" "2009-03-26 13:27:03" "2009-03-26 13:32:03"
> "2009-03-26 13:37:03" "2009-03-26 13:42:03" "2009-03-26 13:47:03"
> [31] "2009-03-26 13:52:03" "2009-03-26 13:57:04" "2009-03-26 14:01:02"
> "2009-03-26 14:06:05" "2009-03-26 14:11:05" "2009-03-26 14:16:06"
> [37] "2009-03-26 14:21:06" "2009-03-26 14:26:08" "2009-03-26 14:31:09"
> "2009-03-26 14:36:10" "2009-03-26 14:41:10" "2009-03-26 14:46:15"
> [43] "2009-03-26 14:51:15" "2009-03-26 14:56:15" "2009-03-26 15:01:15"
> "2009-03-26 15:06:17" "2009-03-26 15:11:17" "2009-03-26 15:16:19"
> [49] "2009-03-26 15:21:19" "2009-03-26 15:26:19" "2009-03-26 15:31:22"
> "2009-03-26 15:36:23" "2009-03-26 15:41:24" "2009-03-26 15:46:24"
> [55] "2009-03-26 15:51:25" "2009-03-26 15:56:25" "2009-03-26 16:01:25"
> "2009-03-26 16:06:26" "2009-03-26 16:11:26" "2009-03-26 16:16:26"
> [61] "2009-03-26 16:21:27" "2009-03-26 16:26:27" "2009-03-26 16:31:28"
> "2009-03-26 16:36:28" "2009-03-26 16:41:29" "2009-03-26 16:46:30"
> [67] "2009-03-26 16:51:31" "2009-03-26 16:56:31" "2009-03-26 17:01:32"
> "2009-03-26 17:06:32" "2009-03-26 17:11:33" "2009-03-26 17:16:33"
> [73] "2009-03-26 17:21:33" "2009-03-26 17:26:35" "2009-03-26 17:31:36"
> "2009-03-26 17:36:36" "2009-03-26 17:41:36" "2009-03-26 17:46:36"
> [79] "2009-03-26 17:51:39" "2009-03-26 17:56:40" "2009-03-26 18:01:40"
> "2009-03-26 18:06:40" "2009-03-26 18:11:40" "2009-03-26 18:16:40"
> [85] "2009-03-26 18:21:41" "2009-03-26 18:26:41" "2009-03-26 18:31:41"
> "2009-03-26 18:36:41" "2009-03-26 18:41:41" "2009-03-26 18:46:41"
> [91] "2009-03-26 18:51:42" "2009-03-26 18:56:42" "2009-03-26 19:06:42"
>>
>> as.numeric(diff(strptime(datajour$Date, format="%Y-%m-%d %H:%M:%S"),
>> units="mins"))
>  [1]  46 301 581 300 300 300 301 300 300 300 300 300 301 300 300 300 300 300
> 300 301 300 301 300 300 300 300 300 300 300 300 301 238 303 300 301 300 302
> 301
> [39] 301 300 305 300 300 300 302 300 302 300 300 303 301 301 300 301 300 300
> 301 300 300 301 300 301 300 301 301 301 300 301 300 301 300 300 302 301 300
> 300
> [77] 300 303 301 300 300 300 300 301 300 300 300 300 300 301 300 600
>
> ------------------------------------------------------------------------
>> strptime(datajour$Date, format="%Y-%m-%d %H:%M:%S")
>  [1] "2009-03-26 11:22:24" "2009-03-26 11:27:25" "2009-03-26 11:37:04"
> "2009-03-26 11:42:04" "2009-03-26 11:47:04" "2009-03-26 11:52:04"
>  [7] "2009-03-26 11:57:04" "2009-03-26 12:02:05" "2009-03-26 12:07:06"
> "2009-03-26 12:12:06" "2009-03-26 12:17:06" "2009-03-26 12:22:06"
> [13] "2009-03-26 12:27:07" "2009-03-26 12:32:07" "2009-03-26 12:37:07"
> "2009-03-26 12:42:07" "2009-03-26 12:47:07" "2009-03-26 12:52:08"
> [19] "2009-03-26 12:57:08" "2009-03-26 13:02:08" "2009-03-26 13:07:09"
> "2009-03-26 13:12:09" "2009-03-26 13:17:09" "2009-03-26 13:22:09"
> [25] "2009-03-26 13:27:09" "2009-03-26 13:32:09" "2009-03-26 13:37:09"
> "2009-03-26 13:42:09" "2009-03-26 13:47:09" "2009-03-26 13:52:09"
> [31] "2009-03-26 13:57:10" "2009-03-26 14:01:08" "2009-03-26 14:06:11"
> "2009-03-26 14:11:11" "2009-03-26 14:16:12" "2009-03-26 14:21:12"
> [37] "2009-03-26 14:26:15" "2009-03-26 14:31:18" "2009-03-26 14:36:18"
> "2009-03-26 14:41:19" "2009-03-26 14:46:22" "2009-03-26 14:51:22"
> [43] "2009-03-26 14:56:23" "2009-03-26 15:01:24" "2009-03-26 15:06:24"
> "2009-03-26 15:11:24" "2009-03-26 15:16:24" "2009-03-26 15:21:24"
> [49] "2009-03-26 15:26:24" "2009-03-26 15:31:28" "2009-03-26 15:36:29"
> "2009-03-26 15:41:29" "2009-03-26 15:46:30" "2009-03-26 15:51:33"
> [55] "2009-03-26 15:56:33" "2009-03-26 16:01:33" "2009-03-26 16:06:33"
> "2009-03-26 16:11:34" "2009-03-26 16:16:34" "2009-03-26 16:21:35"
> [61] "2009-03-26 16:26:35" "2009-03-26 16:31:35" "2009-03-26 16:36:35"
> "2009-03-26 16:41:35" "2009-03-26 16:46:36" "2009-03-26 16:51:37"
> [67] "2009-03-26 16:56:37" "2009-03-26 17:01:37" "2009-03-26 17:06:38"
> "2009-03-26 17:11:38" "2009-03-26 17:16:38" "2009-03-26 17:21:38"
> [73] "2009-03-26 17:26:40" "2009-03-26 17:31:43" "2009-03-26 17:36:43"
> "2009-03-26 17:41:43" "2009-03-26 17:46:44" "2009-03-26 17:51:45"
> [79] "2009-03-26 17:56:46" "2009-03-26 18:01:46" "2009-03-26 18:06:46"
> "2009-03-26 18:11:47" "2009-03-26 18:16:47" "2009-03-26 18:21:48"
> [85] "2009-03-26 18:26:48" "2009-03-26 18:31:48" "2009-03-26 18:36:48"
> "2009-03-26 18:41:48" "2009-03-26 18:46:48" "2009-03-26 18:51:48"
> [91] "2009-03-26 18:56:48" "2009-03-26 19:01:48"
>>
>> as.numeric(diff(strptime(datajour$Date, format="%Y-%m-%d %H:%M:%S"),
>> units="mins"))
>  [1] 5.016667 9.650000 5.000000 5.000000 5.000000 5.000000 5.016667 5.016667
> 5.000000 5.000000 5.000000 5.016667 5.000000 5.000000 5.000000 5.000000
> [17] 5.016667 5.000000 5.000000 5.016667 5.000000 5.000000 5.000000 5.000000
> 5.000000 5.000000 5.000000 5.000000 5.000000 5.016667 3.966667 5.050000
> [33] 5.000000 5.016667 5.000000 5.050000 5.050000 5.000000 5.016667 5.050000
> 5.000000 5.016667 5.016667 5.000000 5.000000 5.000000 5.000000 5.000000
> [49] 5.066667 5.016667 5.000000 5.016667 5.050000 5.000000 5.000000 5.000000
> 5.016667 5.000000 5.016667 5.000000 5.000000 5.000000 5.000000 5.016667
> [65] 5.016667 5.000000 5.000000 5.016667 5.000000 5.000000 5.000000 5.033333
> 5.050000 5.000000 5.000000 5.016667 5.016667 5.016667 5.000000 5.000000
> [81] 5.016667 5.000000 5.016667 5.000000 5.000000 5.000000 5.000000 5.000000
> 5.000000 5.000000 5.000000
>>
> ------------------------------------------------------------------------
>
> --
> View this message in context: http://www.nabble.com/Results-sometimes-in-seconds-with-difftime-unit%3Dmins-tp22743564p22743564.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help at 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.
>

-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?