See the help page for the difftime() function, which will tell you
how to specify the units of the differences.
(when you don't specify, it chooses the units according to some rules)
-Don
At 4:24 PM -0400 6/14/10, James Rome wrote:>I have two dataframe columns of POXIXct data/times that include seconds.
>I got them into this format using for example
>zsort$ETA <- as.POSIXct(as.character(zsort$ETA), format="%m/%d/%Y
%H:%M:%S")
>
>My problem is that when I subtract the two columns, sometimes the
>difference is given in seconds, and sometimes it is given in minutes. I
>don't care which it is, but I need to know which one I will get.
>
>DateTime ETA
>2010-05-16 02:19:56 2010-05-16 03:46:35
>...
>Browse[1]> mins = zsort$ETA - zsort$DateTime
>Browse[1]> mins
>Time differences in hours
> [1] 1.444167 2.685000 3.077222 3.210278 3.248056 3.281944 3.281944
>3.360278 3.360278 3.582778 4.574444 5.506111 5.857778 6.150278 6.150278
>6.243056 6.243889 6.248056 6.248611 6.248611 6.356667
>attr(,"tzone")
>
>But sometimes the answer is in seconds.
># make a column with the minutes before landing
>>zsort$MinBeforeLand = zsort$ETA - zsort$DateTime
>> zsort$MinBeforeLand
>Time differences in secs
> [1] -50 136 221 878 1192 2263 3296 3959 4968 5846 8709
>11537 12198 12442 12642 15952 18273 19952 20538
>
>How do I specify the resultant units?
>
>Thanks,
>Jim Rome
>
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--
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062