[R] ifelse strips POSIXct class from object

[Duncan Murdoch]

On 11-06-05 8:49 AM, Denis Chabot wrote:
> Thanks Duncan, I'll go back to if and else!

Be careful, it might not give you the same answer.

I'd use this variation on the advice from ?ifelse:

new.date <- my.date + x
new.date[is.na(my.date)] <- min(default.date) + x

The thing to watch out for in this construction is that the lengths of 
the vectors come out right.  I'm assuming that my.date + x is the same 
length as is.na(my.date)], and that min(default.date) + x is length 1, 
but I haven't tried your code to check.

Duncan Murdoch

>
> Denis
> Le 2011-06-05 à 08:39, Duncan Murdoch a écrit :
>
>> On 11-06-05 8:23 AM, Denis Chabot wrote:
>>> Hi,
>>>
>>> I was "losing" my dates in a script and upon inspection, found that my recent switch from separate "if" and "else" to "ifelse" was the cause. But why?
>>
>> See ?ifelse.  The class of the result is the same as the class of the test, not the classes of the alternatives.  You need to manually attach the class again, or use a different construction.
>>
>> Duncan Murdoch
>>
>>>
>>> my.date	= as.POSIXct("2011-06-04 08:00:00")
>>> default.date = seq(as.POSIXct("2011-01-01 08:00:00"), as.POSIXct("2011-09-01 08:00:00"), length=15)
>>> x = 4 * 60 * 60
>>> (my.date + x)
>>> (min(default.date) + x)
>>> (new.date = ifelse(!is.na(my.date), my.date + x, min(default.date) + x)	)
>>>
>>> (if(!is.na(my.date)) new.date2 = my.date + x  else new.date2= min(default.date) + x	)
>>>
>>> On my machine, new.date is "numeric" whereas new.date2 is "POSIXct" and "POSIXt", as desired.
>>>
>>> sessionInfo()
>>> R version 2.13.0 (2011-04-13)
>>> Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)
>>>
>>> locale:
>>> [1] fr_CA.UTF-8/fr_CA.UTF-8/C/C/fr_CA.UTF-8/fr_CA.UTF-8
>>>
>>> attached base packages:
>>> [1] stats     graphics  grDevices utils     datasets  methods   base
>>>
>>>
>>> Thanks in advance,
>>>
>>> Denis
>>> ______________________________________________
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>>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>>> and provide commented, minimal, self-contained, reproducible code.
>>
>