[R] strange behaviour of "POSIXlt" "POSIXt" object

[ikuzar]

Hi, 

I do not know what part of my code should I post here (I use large size of
data, the loop "for" contains many lines). The situation is difficult to
post here, but I hope these lines would be useful for help:

hcEndDateTmp = userDateStart
  if((hcStartTime<="23:59") & (hcEndTime >= "00:00")){
    hcEndDateTmp$mday = userDateStart$mday + 1
  }
  hcEndDate = strftime(hcEndDateTmp, "%Y-%m-%d")
  hcStart = ""
hcEnd = as.POSIXlt(paste(hcEndDate, hcEndTime))

for(rowNum in 1:nbJour){
    ...
    hcStart = as.POSIXlt(ecs$startAt[[rowNum]])
    ecsInterval2 =
datePower[(datePower$DateTime>=hcStart)&(datePower$DateTime<=hcEnd), ]
    ...
   hcEnd$mday = hcEnd$mday + 1
  cat("DEBUG: rowNum=", rowNum, "is.na(hcEnd)=", is.na(hcEnd), "\n")
}

the two last lines are very important. It yields:

DEBUG: rowNum= 1 is.na(hcEnd)= FALSE 
DEBUG: rowNum= 2 is.na(hcEnd)= FALSE 
DEBUG: rowNum= 3 is.na(hcEnd)= FALSE 
DEBUG: rowNum= 4 is.na(hcEnd)= FALSE 
DEBUG: rowNum= 5 is.na(hcEnd)= FALSE 
DEBUG: rowNum= 6 is.na(hcEnd)= FALSE 
DEBUG: rowNum= 7 is.na(hcEnd)= TRUE 

Browse[1]> hcEnd
[1] "2009-03-29 06:30:00"
Browse[1]> class(hcEnd)
[1] "POSIXlt" "POSIXt" 

So, At the end of 7th iteration, hcEnd becomes NA (I guess because of
hcEnd$mday = hcEnd$mday + 1 ?!?). But It remains strange because the class
of hcEnd is here "POSIXlt" "POSIXt" (it should be "logical".!! Am I
wrong???)

Here is the version of R:
platform       i386-pc-mingw32              
arch           i386                         
os             mingw32                      
system         i386, mingw32                
status                                      
major          2                            
minor          13.2                         
year           2011                         
month          09                           
day            30                           
svn rev        57111                        
language       R                            
version.string R version 2.13.2 (2011-09-30)

thanks for your help

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