[R] Converting strings to date

[Roger D. Peng]

You need to be more specific when you say "it works" =)  strptime() 
returns a POSIXlt object whose printed representation appears to be a 
string (but it is a list).  What you want, I think, is either 
as.POSIXct() or as.Date().  See ?DateTimeClasses.

-roger

João Mendes Moreira wrote:
> Hello,
> 
> I have the following problem:
> test is a data frame with 9 fields. The field test$Date is factorized with dates. The format is dd-mm-yyyy (using Oracle notation). I want to convert this to Date in '%Y-%m-%d format.
> What I am doing is:
> for (i in 1:nrow(test))
>   {
>    test[i,]$Data<-strptime(substring(test[i,]$Data,1,10),"%d-%m-%Y")
>   }
> 
> test is a data frame. 
> 
> The error is:
> Error in "$<-.data.frame"(`*tmp*`, "Data", value = list(sec = 0, min = 0,  : 
>         replacement has 9 rows, data has 1
> 
> But if I do:
> strptime(substring(test[1:nrow(teste),]$Data,1,10),"%d-%m-%Y")
> it works! Why the assignement does not work?
> 
> Thanks
> 
> Joao Moreira
> 	[[alternative HTML version deleted]]
> 
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-- 
Roger D. Peng
http://www.biostat.jhsph.edu/~rpeng/