Thanks, add as.Date('1970-01-01') to the result column works.
Richard
-----Original Message-----
From: David Winsemius [mailto:dwinsem...@comcast.net]
Sent: Monday, November 22, 2010 3:51 PM
To: Tan, Richard
Cc: r-help@r-project.org
Subject: Re: [R] aggregate a Date column does not work?
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]]
>
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David Winsemius, MD
West Hartford, CT
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