[R] Subtracting POSIXct data/times

[James Rome]

That fixed it. Dumb me. I had assumed that the subtraction of the raw
POSIXcts would always give the same results.

Thanks,
Jim

On 6/14/10 5:22 PM, Don MacQueen wrote:
> 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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>
>