[R] strange problem with strptime and date variable

[Edwin Sun]

Hello all,

I am manipulating a large database with 70,000 records. "strptime" generates
a date variable but R treats some of the values as NA. I attach a simple
example below.

I have spent hours on this problem. Any hint would be greatly appreciated.

Many thanks,

Edwin Sun

# =======start of sample code =============

> x <- c("2005-04-02 19:03:00", "2005-04-03 02:00:00", "2005-04-03
> 14:25:00")
 
> y <- strptime(x, format="%Y-%m-%d %H:%M:%S")
 
> x; y; str(x); str(y)
[1] "2005-04-02 19:03:00" "2005-04-03 02:00:00" "2005-04-03 14:25:00"
[1] "2005-04-02 19:03:00" "2005-04-03 02:00:00" "2005-04-03 14:25:00"
 chr [1:3] "2005-04-02 19:03:00" "2005-04-03 02:00:00" ...
 POSIXlt[1:3], format: "2005-04-02 19:03:00" "2005-04-03 02:00:00" ...

> is.na(y)
[1] FALSE  TRUE FALSE

> difftime(y[2], y[1], units="mins")
Time difference of NA mins
 
> difftime(y[3], y[1], units="mins")
Time difference of 1102 mins
 
> sessionInfo()
R version 2.13.1 (2011-07-08)
Platform: i386-pc-mingw32/i386 (32-bit)

locale:
[1] LC_COLLATE=English_United States.1252 
[2] LC_CTYPE=English_United States.1252   
[3] LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C                          
[5] LC_TIME=English_United States.1252    

attached base packages:
[1] grDevices datasets  splines   graphics  stats     tcltk     utils    
[8] methods   base     

other attached packages:
[1] svSocket_0.9-51 TinnR_1.0.3     R2HTML_2.2      Hmisc_3.8-3    
[5] survival_2.36-9

loaded via a namespace (and not attached):
[1] cluster_1.14.0  grid_2.13.1     lattice_0.19-30 svMisc_0.9-61  
[5] tools_2.13.1   

# My computer is 64 bit / Microsoft Window 7; R 2.13.1 (32 bit)

# ======= end of sample code ====================




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