[R] reformat time from hhmm

[William Dunlap]

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Peter Moore
> Sent: Thursday, June 03, 2010 2:22 PM
> To: r-help at r-project.org
> Subject: [R] reformat time from hhmm
> 
> Hi,
> I'm newish to R, a recent convert from Matlab... So far I'm 
> impressed, and
> determined to solve the following problem, which seems like 
> it should be
> easy:
> I have a long (millions of points) data series recorded with 
> a datalogger
> that produced a timestamp in 4 columns: Year, Day of Year, 
> Time in (H)HMM
> and Seconds.  I would like to have R interpret these columns as a time
> object and have made some progress (e.g., using paste() to 
> create a single
> column and then strptime() to interpret -- is that too 
> roundabout??), but
> one thing is throwing me off and I can't seem to conquer it.  The
> hour-minute column in the raw data has no colon, so noon 
> looks like "1200".
> Morning times have only 3 characters and afternoon times have 
> 4.  I've been
> playing around with a fake set of times:
>    times <- c(110, 230, 459, 1001, 1238, 1922)
> 
> When I use
>    strptime(data, "%k%M"

You must have done this with 'times', not 'data'.
strptime's first argument should be character data,
not numeric and the default conversion of numeric
to character changes 110->"110", not "0110".  I like
to use sprintf() (with its C syntax) to control the
conversion:

> strptime(sprintf("%04d", times), "%k%M")
[1] "2010-06-03 01:10:00" "2010-06-03 02:30:00" "2010-06-03 04:59:00"
"2010-06-03 10:01:00" "2010-06-03 12:38:00"
[6] "2010-06-03 19:22:00"

You could put the year-month-day part into the sprintf's
format argument as well if you don't want it to use today's
date for that.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com  


> the last three are interpreted fine but the first three are messed up
> because, for some reason, (even though I use %k for hour 
> format?) the first
> two characters are assumed to be hour and the remaining one 
> is minutes.  For
> times[3] I get NA because R doesn't know what to do with 45 hours...
>    [1] "2010-06-03 11:00:00" "2010-06-03 23:00:00" NA
>    [4] "2010-06-03 10:01:00" "2010-06-03 12:38:00" 
> "2010-06-03 19:22:00"
> 
> Fair enough, so I tried a different angle, using an if...else 
> statement:
>    hours <- if(nchar(times)>3) strtrim(times,2) else strtrim(times,1)
> 
> This worked great when times was only a vector of length=1, 
> but when I try
> to apply it to something larger, I get the following warning:
>    Warning message:
>      In  if(nchar(times)>3) strtrim(times,2) else strtrim(times,1)  :
>      the condition has length > 1 and only the first element 
> will be used
> and the output hours are only the first character.  Not 
> entirely sure if I
> understand this.
> 
> Any advice on how to do this?  Are there packages or commands 
> that I'm not
> aware of that know how to deal with (h)hmm times?
> 
> Thanks much,
> -Pete
> ---------------------------------------------
> platform       i486-pc-linux-gnu
> arch           i486
> os             linux-gnu
> system         i486, linux-gnu
> status
> major          2
> minor          10.1
> year           2009
> month          12
> day            14
> svn rev        50720
> language       R
> version.string R version 2.10.1 (2009-12-14)
> 
> -- 
> Pete Moore
> Postdoctoral Research Associate
> Dept. Geological & Atmospheric Sciences
> Iowa State University
> 
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