[R] histogram of time-stamp data

[e-letter]

On 16/07/2012, r-help-request at r-project.org
 <r-help-request at r-project.org> wrote:
 > ------------------------------
 >
 > Message: 77
 > Date: Mon, 16 Jul 2012 10:48:39 +0100
 > From: Rui Barradas <ruipbarradas at sapo.pt>
 > To: e-letter <inpost at gmail.com>
 > Cc: r-help at r-project.org
 > Subject: Re: [R] histogram of time-stamp data
 > Message-ID: <5003E377.3000604 at sapo.pt>
 > Content-Type: text/plain; charset=ISO-8859-1; format=flowed
 >
 >
 > timestamps <- as.POSIXct(Sys.Date()) + sample(24*60*60, 1e3, TRUE)
 >

 Why is it necessary to apply the sample to the current date? Looking
 at the dataframe, I noticed that values have been changed:

 file 'test.txt':
 12:19:00
 09:30:00
 16:56:00
 01:56:00
 10:44:00
 10:31:00
 02:14:00
 05:05:00
 12:52:00
 21:50:00

 R command terminal input:
 > timestamps<-read.table("test.txt")
 > timestamps
          V1
 1  12:19:00
 2  09:30:00
 3  16:56:00
 4  01:56:00
 5  10:44:00
 6  10:31:00
 7  02:14:00
 8  05:05:00
 9  12:52:00
 10 21:50:00
 > timestamps <- as.POSIXct(Sys.Date()) + sample(24*60*60, 1e3, TRUE)
 > write.csv(timestamps,file="test1.txt")

 test1.txt:
 "","x"
 "1",2012-07-16 04:52:48
 "2",2012-07-16 21:21:28
 "3",2012-07-16 18:58:27
 "4",2012-07-16 22:17:25
 "5",2012-07-16 11:13:52
 "6",2012-07-16 03:17:35
 "7",2012-07-16 02:14:17
 "8",2012-07-16 14:18:27
 "9",2012-07-16 14:39:16

 Why is this happening?