[R] read "4-jan-02" as date

[Sundar Dorai-Raj]

bogdan romocea wrote:

> Dear R users,
> 
> I have a column with dates (character) in a data frame:
> 12-Jan-01 11-Jan-01 10-Jan-01 9-Jan-01  8-Jan-01  5-Jan-01
> and I need to convert them to (Julian) dates so that I can
> sort the whole data frame by date. I thought it would be
> very simple, but after checking the documentation and the
> list I still don't have something that works.
> 
> 1. as.Date returns the error below. What am I doing wrong?
> As far as I can see the character strings are in standard
> format.
> d$Date <- as.Date(d$Date, format="%d-%b-%y")
> Error in fromchar(x) : character string is not in a
> standard unambiguous format
> 
> 2. as.date {Survival} produces this error,
> d$Date <- as.date(d$Date, order = "dmy")
> Error in as.date(d$Date, order = "dmy") : Cannot coerce to
> date format
> 
> 3. Assuming all else fails, is there a text function
> similar to SCAN in SAS? Given a string like "9-Jan-01" and
> "-" as separator, I'd like a function that can read the
> first, second and third values (9, Jan, 01), so that I can
> get Julian dates with mdy.date {survival}.
> 
> Thanks in advance,
> b.
> 

If you're reading this from a file (via read.table, for example), then 
your date column is probably a factor. Convert to character first.

 > x
[1] 12-Jan-01 11-Jan-01 10-Jan-01 9-Jan-01  8-Jan-01  5-Jan-01
Levels: 10-Jan-01 11-Jan-01 12-Jan-01 5-Jan-01 8-Jan-01 9-Jan-01
 >
 > Date(x, format="%d-%b-%y")
Error in fromchar(x) : character string is not in a standard unambiguous 
format
 >
 > sort(as.Date(as.character(x), format="%d-%b-%y"))
[1] "2001-01-05" "2001-01-08" "2001-01-09" "2001-01-10" "2001-01-11"
[6] "2001-01-12"


--sundar