No "number of days" format for 'difftime'?

Mon, Aug 8, 2016 7:43 AM

Martin Maechler <maechler at stat.math.ethz.ch> writes:

Loris Bennett <loris.bennett at fu-berlin.de>
    on Mon, 8 Aug 2016 14:12:47 +0200 writes:

    > Loris Bennett <loris.bennett at fu-berlin.de> writes:

    >> Thanks for the link, John.  However, there is a hyphen missing.  It
    >> should be:
    >> 
    >> http://www.dummies.com/how-to/content/how-to-read-errors-and-warnings-in-r.html
    >> 
    >> Appropriately, with the correct URL we find the too often forgotten
    >> pearl of wisdom:
    >> 
    >> "Chances are, you just typed something wrong there."
    >> 
    >> I think I need this on my coffee cup.
    >> 
    >> Cheers,
    >> 
    >> Loris

    > Continuing the topic for my future self and others equally poorly versed
    > in The Art and Dark Science of Interpreting R Error Messages, if I have
    > the following in the file "my_data"

    > 1094165      2016-07-24T09:40:02 13-23:03:28          1  COMPLETED 
    > 1112076      2016-08-01T14:45:49 6-13:26:15          1  COMPLETED

    > and do

    >> d <- read.table("my_data")
    >> colnames(d) <- c("jobid","start","elapsed","alloccpus","state")
    >> df <- transform(d,start = as.POSIXct(start,format="%Y-%m-%dT%H:%M:%S"),elapsed = as.difftime(elapsed,format="%d-%H:%M:%S"))

    > I get the following:

    > Error in as.difftime(elapsed, format = "%d-%H:%M:%S") : 
    > 'tim' is not character or numeric

Well, let me argue that you should have found this to be a *helpful*
error message. You are no complete beginner anymore, right,
so

1) the error is in your use of  as.difftime().

2) ?as.difftime  or  str(difftime)
   both clearly indicate that  'tim' is the first argument of as.difftime,

and I really do wonder why you continued with the infamous
"trial-and-error programming technique" instead of reading or at
least quickly browsing the relevant reference, i.e., help page

Martin

My apologies, you are absolutely right - I see the error of my ways.
The only feeble defence I can mount is that the usage example from
?as.difftime

  as.difftime(tim, format = "%X", units = "auto")

superficially disguises the fact that the first argument is also a named
argument with the name 'tim'.  I think I had assumed that the initial
argument were always positional, e.g. as for paste0

  paste0(..., collapse = NULL)

However, I now realise that '...' also generates named arguments, e.g.

  paste0(..1='a',..2='b')

So as a non-beginner but infrequent R user, in future I shall try use
the explicit form more often, e.g.

  as.difftime(tim = "4-03:02:01", format = "%d-%H:%M:%S")

to remind myself what I am doing.

So fortune(350) really is true.  I just didn't believe enough to read
enough. 

Loris

Dr. Loris Bennett (Mr.)
ZEDAT, Freie Universit?t Berlin         Email loris.bennett at fu-berlin.de

No "number of days" format for 'difftime'?

Thread (9 messages)