[Rd] diff(time) vs. difftime?

Spencer Graves
Mon, 19 Mar 2012 22:27:10 -0000

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 Jos?, CA 95126
ph:  408-655-4567
web:  www.structuremonitoring.com