On Nov 22, 2010, at 3:54 PM, Tan, Richard wrote:
Thanks, add as.Date('1970-01-01') to the result column works.
But that should make them all the same date in 1970. Since aggregate
renames the date column to "x", this should work:
as.Date( aggregate(a$payday, list(a$name), max)$x )
[1] "2000-01-01" "1999-01-01"
Richard
-----Original Message-----
From: David Winsemius [mailto:dwinsem...@comcast.net]
Sent: Monday, November 22, 2010 3:51 PM
To: Tan, Richard
Cc: r-help@r-project.org
Subject: Re: [R] aggregate a Date column does not work?
On Nov 22, 2010, at 3:39 PM, Tan, Richard wrote:
Hi, I am trying to aggregate max a Date type column but have weird
result, how do I fix this?
In the process of getting max() you coerced the Dates to numeric and
now you need to re-coerce them back to Dates
?as.Date
as.Date(<your result>) (possibly with an origin it the default
"1970-01-01" doesn't get used.
--
David.
a <- rbind(
+ data.frame(name='Tom', payday=as.Date('1999-01-01')),
+ data.frame(name='Tom', payday=as.Date('2000-01-01')),
+ data.frame(name='Pete', payday=as.Date('1998-01-01')),
+ data.frame(name='Pete', payday=as.Date('1999-01-01'))
+ )
a
name payday
1 Tom 1999-01-01
2 Tom 2000-01-01
3 Pete 1998-01-01
4 Pete 1999-01-01
aggregate(a$payday, list(a$name), max)
Group.1 x
1 Tom 10957
2 Pete 10592
Thanks,
Richard
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David Winsemius, MD
West Hartford, CT
David Winsemius, MD
West Hartford, CT
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and provide commented, minimal, self-contained, reproducible code.
