[R] aggregate a Date column does not work?

David Winsemius dwinsemius at comcast.net
Mon Nov 22 21:50:33 CET 2010


On Nov 22, 2010, at 3:39 PM, Tan, Richard wrote:

> Hi, I am trying to aggregate max a Date type column but have weird
> result, how do I fix this?

In the process of getting max() you coerced the Dates to numeric and  
now you need to re-coerce them back to Dates

?as.Date
as.Date(<your result>)  (possibly with an origin it the default  
"1970-01-01" doesn't get used.

-- 
David.
>
>
>
>> a <- rbind(
>
> + data.frame(name='Tom', payday=as.Date('1999-01-01')),
>
> + data.frame(name='Tom', payday=as.Date('2000-01-01')),
>
> + data.frame(name='Pete', payday=as.Date('1998-01-01')),
>
> + data.frame(name='Pete', payday=as.Date('1999-01-01'))
>
> + )
>
>> a
>
>  name     payday
>
> 1  Tom 1999-01-01
>
> 2  Tom 2000-01-01
>
> 3 Pete 1998-01-01
>
> 4 Pete 1999-01-01
>
>> aggregate(a$payday, list(a$name), max)
>
>  Group.1     x
>
> 1     Tom 10957
>
> 2    Pete 10592
>
>
>
> Thanks,
>
> Richard
>
>
>
>
> 	[[alternative HTML version deleted]]
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.

David Winsemius, MD
West Hartford, CT



More information about the R-help mailing list