R help - Mar 2009 - Extract dates from dataframe

Hi,

I have the following dataframe:
   ID                            Dates
  1               16-07-01  06-10-95
  2            24/01/02     06-10-95
  3 16/01/02   16/08/94     12/01/91

And I would like to extract the dates, but couple the ID's to the right
dates, eg:
ID  Dates
1    16-07-01
1    06-10-95
2    24-01-02
2  ....

I have no clue about how to get started, looks something for the
regexp/grep/... kind of functions, but I don't get the point.

Any thoughts??

Kind regards

Bart Joosen

PS: for the reconstruction of the dataframe:
dat <-
structure(list(ID = c(1, 2, 3), Dates = structure(c(2L, 4L, 6L
), .Label = c("16-01-02   16-08-94", "16-07-01  06-10-95",
"24-01-02
06-10-95", 
"24/01/02     06-10-95", "16/01/02   16/08/94",
"16/01/02   16/08/94
12/01/91"
), class = "factor")), .Names = c("ID", "Dates"),
row.names = c(NA,
3L), class = "data.frame")


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Try this:

library(gsubfn)

# convert date strings to dd-mm-yy
Dates <- gsub("/", "-", dat$Dates)

# regular expressiont to match dates
re <- "\\d\\d-\\d\\d-\\d\\d"

# extract dates and convert them to Date class
# giving a list d each of whose components is a vector of dates
d <- strapply(Dates, re, ~ as.Date(x, "%d-%m-%y"), perl = TRUE)
names(d) <- dat$ID

# combine them into a single data frame
do.call(rbind, lapply(dat$ID, function(id) data.frame(ID = id, Date = d[[id]])))

On Fri, Mar 6, 2009 at 6:17 AM, bartjoosen <bartjoosen at hotmail.com>
wrote:
>
> Hi,
>
> I have the following dataframe:
> ? ID ? ? ? ? ? ? ? ? ? ? ? ? ? ?Dates
> ?1 ? ? ? ? ? ? ? 16-07-01 ?06-10-95
> ?2 ? ? ? ? ? ?24/01/02 ? ? 06-10-95
> ?3 16/01/02 ? 16/08/94 ? ? 12/01/91
>
> And I would like to extract the dates, but couple the ID's to the right
> dates, eg:
> ID ?Dates
> 1 ? ?16-07-01
> 1 ? ?06-10-95
> 2 ? ?24-01-02
> 2 ?....
>
> I have no clue about how to get started, looks something for the
> regexp/grep/... kind of functions, but I don't get the point.
>
> Any thoughts??
>
> Kind regards
>
> Bart Joosen
>
> PS: for the reconstruction of the dataframe:
> dat <-
> structure(list(ID = c(1, 2, 3), Dates = structure(c(2L, 4L, 6L
> ), .Label = c("16-01-02 ? 16-08-94", "16-07-01
?06-10-95", "24-01-02
> 06-10-95",
> "24/01/02 ? ? 06-10-95", "16/01/02 ? 16/08/94",
"16/01/02 ? 16/08/94
> 12/01/91"
> ), class = "factor")), .Names = c("ID",
"Dates"), row.names = c(NA,
> 3L), class = "data.frame")
>
>
> --
> View this message in context:
http://www.nabble.com/Extract-dates-from-dataframe-tp22369479p22369479.html
> Sent from the R help mailing list archive at Nabble.com.
>
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> PLEASE do read the posting guide
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