[R] cut POSIX results in NA - bug?

[Gabor Grothendieck]

Petr Pikal <petr.pikal <at> precheza.cz> writes:

: 
: Dear all
: 
: I try to make hourly average by cut() function, which almost works 
: as *I* expected. What puzled me is that if there is only one item at 
: the end of your data it results in NA.
: 
: Example will explain what I mean
: 
: datum<-seq(ISOdate(2004,8,31), ISOdate(2004,9,1), "min")
: 
: cut(datum[1370:1381],"hour", labels=F)
:  [1]  1  1  1  1  1  1  1  1  1  1  1 NA
: 
: cut(datum[1370:1382],"hour", labels=F)
:  [1] 1 1 1 1 1 1 1 1 1 1 1 2 2
: 
: I do not understand why the last item in first call is NA. I found it 
: only when there was a switch from DST to standard time as it 
: coused a trouble in one of my functions and I found there is NA 
: value where I did not expected it. 
: 
: I can make some workaround but can you please explain me why 
: first call results in NA value at the end of a vector and if it is 
: *intended* behaviour. If yes I can count with it in improvement of 
: my function(s), if not I can make some temporary workaround.
: 

Your question has already been answered but here is an alternate
approach that avoids cut.  We format the datetimes and truncate each 
string at the hour, make that a factor and then get the integer codes:

R> cutHour <- function(x) as.integer(factor(substring(format(x),1,13)))
R> cutHour(datum[1370:1381])
 [1] 1 1 1 1 1 1 1 1 1 1 1 2
R> cutHour(datum[1370:1382])
 [1] 1 1 1 1 1 1 1 1 1 1 1 2 2