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

[jim holtman]

Here is an example of converting the 'date' your dataframe to 'time'
(POSIXct) and then taking the first 'time' and creating the 5 previous days
from that date:

   id      date case
1   1 27apr1993    1
2   2 13feb2005    1
3   3 29may2002    1
4   4 22sep2005    1
5   5 18dec1991    1
6   6 07jun2010    1
7   7 07jul1991    1
8   8 04feb2008    1
9   9 31jan2005    1
10 10 01feb2003    1
11 11 29jan2009    1
12 12 03mar2008    1
> ?strptime
> x$time <- as.POSIXct(x$date, format = "%d%b%Y")
> x
   id      date case       time
1   1 27apr1993    1 1993-04-27
2   2 13feb2005    1 2005-02-13
3   3 29may2002    1 2002-05-29
4   4 22sep2005    1 2005-09-22
5   5 18dec1991    1 1991-12-18
6   6 07jun2010    1 2010-06-07
7   7 07jul1991    1 1991-07-07
8   8 04feb2008    1 2008-02-04
9   9 31jan2005    1 2005-01-31
10 10 01feb2003    1 2003-02-01
11 11 29jan2009    1 2009-01-29
12 12 03mar2008    1 2008-03-03
> seq(x$time[1], by = '-1 day', length = 5)
[1] "1993-04-27 EDT" "1993-04-26 EDT" "1993-04-25 EDT" "1993-04-24 EDT"
"1993-04-23 EDT"
>

You can do the same thing for the dataframe:

> lapply(x$time, function(a) seq(a, by = '-1 day', length = 5))
[[1]]
[1] "1993-04-27 EDT" "1993-04-26 EDT" "1993-04-25 EDT" "1993-04-24 EDT"
"1993-04-23 EDT"

[[2]]
[1] "2005-02-13 EST" "2005-02-12 EST" "2005-02-11 EST" "2005-02-10 EST"
"2005-02-09 EST"

[[3]]
[1] "2002-05-29 EDT" "2002-05-28 EDT" "2002-05-27 EDT" "2002-05-26 EDT"
"2002-05-25 EDT"

[[4]]
[1] "2005-09-22 EDT" "2005-09-21 EDT" "2005-09-20 EDT" "2005-09-19 EDT"
"2005-09-18 EDT"
.......



Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?
Tell me what you want to do, not how you want to do it.

On Thu, Dec 11, 2014 at 10:54 AM, Kuma Raj <pollaroid at gmail.com> 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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