[R] Create previous dates from date with consideration of leap year

[Lee, Chel Hee]

The sample data you provided has the variable 'date'.  Since the type of 
this variable is 'factor', you may try to convert type of variable from 
'factor' to 'date' as shown in the below:

 > x$rval <- as.Date(x$date, format="%d%b%Y")-5
 > x
    id      date case       rval
1   1 27apr1993    1 1993-04-22
2   2 13feb2005    1 2005-02-08
3   3 29may2002    1 2002-05-24
4   4 22sep2005    1 2005-09-17
5   5 18dec1991    1 1991-12-13
6   6 07jun2010    1 2010-06-02
7   7 07jul1991    1 1991-07-02
8   8 04feb2008    1 2008-01-30
9   9 31jan2005    1 2005-01-26
10 10 01feb2003    1 2003-01-27
11 11 29jan2009    1 2009-01-24
12 12 03mar2008    1 2008-02-27
 >

Leap year is also considered (See the last case 'id=12').  Is this what 
you are looking for?   I hope this helps.

Chel Hee Lee

On 12/11/2014 9:54 AM, Kuma Raj wrote:
> Dear R Community,
>
> I wish to create 5 preceding dates from the date variable by ID. How
> could I create such dates? The code should consider leap year.
>
> Thanks
>
> Sample data follows:
>
>
> structure(list(id = 1:12, date = structure(c(9L, 6L, 11L, 8L,
> 7L, 5L, 4L, 3L, 12L, 1L, 10L, 2L), .Label = c("01feb2003", "03mar2008",
> "04feb2008", "07jul1991", "07jun2010", "13feb2005", "18dec1991",
> "22sep2005", "27apr1993", "29jan2009", "29may2002", "31jan2005"
> ), class = "factor"), case = c(1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,
> 1L, 1L, 1L, 1L)), .Names = c("id", "date", "case"), class =
> "data.frame", row.names = c(NA,
> -12L))
>
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