[R] diff of two timestamps

[William Dunlap]

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of sugo
> Sent: Wednesday, September 02, 2009 4:51 PM
> To: r-help at r-project.org
> Subject: [R] diff of two timestamps
> 
> 
> Hi all,
> 
> I have the following problem: I have a csv-file consisting of 
> timestamp
> values (no dates), e.g.:
> Timestamp1;Timestamp2;
> 05:24:43;05:25:05;
> 15:47:02;15:47:22;
> 18:36:05;18:36:24;
> 15:21:24;15:22:04;
> 
> I need a vector with the difference of the two timestamps, so 
> I read the
> data with the read.csv-function:
> myObj <- read.csv("file.csv",header=TRUE,sep=";").
> 
> I have then tried unsuccessfully to convert the data to time 
> format (e.g.
> using the strptime function like date1 <-
> strptime(myObj[0],format="%H:%M:%S")) to be able to perform a datediff
> operation.

R indices start at 1, not 0, and you should use myObj[,1]
to refer to the first column (myObj[1] means a data.frame
containing one column, myObj[,1] means the first column
itself).  myObj$Timestamp1 and myObj[,"Timestamp1"]
give that column as well.

Hence if you want to use numerical indices try

  > strptime(myObj[,1],format="%H:%M:%S")
  [1] "2009-09-02 05:24:43" "2009-09-02 15:47:02" "2009-09-02 18:36:05"
  [4] "2009-09-02 15:21:24"

but replacing the myObj[,1] with myObj$Timestamp1 will
make things clearer.  with() lets you save some typing by
eliminating the repeated mObj$'s.

  > with(myObj, strptime(Timestamp2,format="%H:%M:%S") -
  +                   strptime(Timestamp1,format="%H:%M:%S"))
  Time differences in secs
  [1] 22 20 19 40
  attr(,"tzone")
  [1] ""

Bill Dunlap
TIBCO Software Inc - Spotfire Division
wdunlap tibco.com 

> 
> I would be very grateful if anybody could give me some assistance.
> 
> Thanks in advance,
> Ieyasu
> -- 
> View this message in context: 
> http://www.nabble.com/diff-of-two-timestamps-tp25267603p25267603.html
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide 
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>