[Rd] diff(time) vs. difftime?

From: Spencer Graves <spencer.graves_at_structuremonitoring.com>
Date: Mon, 19 Mar 2012 15:27:10 -0700

       I just encountered another RTFM problem: With diff(as.POSIXct(...), ...) I was unable to control the units of the results. Examples:

> (d.d <- diff(as.POSIXct(c('2012-12-12', '2012-12-13'))))
Time difference of 1 days
> (d.h <- diff(as.POSIXct(c('2012-12-12 08:00', '2012-12-12 09:00'))))
Time difference of 1 hours
> (d.m <- diff(as.POSIXct(c('2012-12-12 08:00', '2012-12-12 08:01'))))
Time difference of 1 mins
> (d.s <- diff(as.POSIXct(c('2012-12-12 08:00:00', '2012-12-12
08:00:01'))))
Time difference of 1 secs
> as.numeric(d.d)

[1] 1
> as.numeric(d.s)

[1] 1

       methods('diff') identified the following:

[1] diff.Date diff.default diff.POSIXt diff.ts diff.zoo*

       In looking at the help pages for each of these functions, I found no mention of "difftime" or any other way to control the units.

  methods('-')
[1] -.Date -.POSIXt -.yearmon* -.yearqtr*

        ?"-.Date" didn't seem helpful on this, either. ?"-.POSIXt" contained a link to "difftime", but I didn't see that until after I read the code for "-.POSIXt" and found "difftime".

       I humbly beseech ye to consider adding a difftime example to all these help pages.

       Thanks,
       Spencer


p.s. In case there is any doubt, I very much appreciate all the work that the R Core team has invested in making R what it is today.

-- 
Spencer Graves, PE, PhD
President and Chief Technology Officer
Structure Inspection and Monitoring, Inc.
751 Emerson Ct.
San Josť, CA 95126
ph:  408-655-4567
web:  www.structuremonitoring.com

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Received on Mon 19 Mar 2012 - 22:30:48 GMT

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