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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