how to choose dates data?

They are really good methods. Thank you very much.
Could I ask one more question. Is there obvious difference between these 
two methods?

2013/7/4 Prof Brian Ripley <ripley at stats.ox.ac.uk 
<mailto:ripley at stats.ox.ac.uk>>

    On 04/07/2013 08:04, Dante.py wrote:

        I have a method which is not so smart --use grep to match the
        pattern.
        for example:
        dates <- c("02/27/92", "02/27/92", "01/14/92", "02/28/92",
        "02/01/91")
        day <- as.Date(dates, "%m/%d/%y")
        day:
        [1] "1992-02-27" "1992-02-27" "1992-01-14" "1992-02-28" "1991-02-01"
        If I want to search for 1991, I can use:
        grep("1991-*", day)


        Hope for a better solution.


    Here are 2.  The first is quite obvious, the second is faster but
    needs more knowledge.

    x <- format(day, "%Y")
    day[x >= "2007" & x <= "2009"]

    x <- as.POSIXlt(day)$year + 1900
    day[x >= 2007 & x <= 2009]




        2013/7/4 Gallon Li <gallon.li at gmail.com
        <mailto:gallon.li at gmail.com>>

            i have converted my data into date format like below:

                day=as.Date(originaldate,"%m/%__d/%Y")
                day[1:5]

            [1] "2008-04-12" "2011-07-02" "2011-09-02" "2008-04-12"
            "2008-04-12"

            I wish to select only those observations from 2007 to 2009,
            how can I
            select from this list?

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