[R] datetime data and plotting

[Don MacQueen]

I do see the described behavior, on three systems, linux R 1.8.0, Mac 
OS X R 1.8.0, and Solaris R 1.7.1.
Plot 1 is different than plot 2; in plot 1 the points are offset to 
the left of the axis tick marks.

datet <- as.POSIXct(dates)

## 1
plot(datet,WEIGHT.KG)

## 2
plot(datet,WEIGHT.KG,xaxt='n')
axis.POSIXct(1,at=datet)

To investigate a bit, I made a copy of axis.POSIXct and modified it 
slightly to return the value of "at" that it calculates. I get this:
"2003-10-06 17:00:00 PDT" "2003-10-08 17:00:00 PDT"
"2003-10-10 17:00:00 PDT" "2003-10-12 17:00:00 PDT"
"2003-10-14 17:00:00 PDT"

These are equal to midnight GMT, since my systems are currently in 
PDT, i.e. GMT-7.


>  version
          _                       
platform powerpc-apple-darwin6.7.5
arch     powerpc                 
os       darwin6.7.5             
system   powerpc, darwin6.7.5    
status   Patched                 
major    1                       
minor    8.0                     
year     2003                    
month    10                      
day      13                      
language R                       


>  version
          _               
platform i686-pc-linux-gnu
arch     i686            
os       linux-gnu       
system   i686, linux-gnu 
status   Patched         
major    1               
minor    8.0             
year     2003            
month    10              
day      16
language R

>  version
          _                  
platform sparc-sun-solaris2.7
arch     sparc              
os       solaris2.7         
system   sparc, solaris2.7  
status                      
major    1                  
minor    7.1                
year     2003               
month    06                 
day      16                 
language R                  


-Don

At 9:21 AM -0400 10/17/03, Jacob Etches wrote:
>If I take the following simple data:
>
>YEAR MONTH DAY WEIGHT.KG
>2003 10 6 1.2
>2003 10 12 1.2
>2003 10 16 1.3
>
>and format the date data and plot it:
>
>dates <- strptime(paste(DAY,MONTH,YEAR),"%d%m%Y")
>plot(c(min(dates),max(dates)),c(0,max(WEIGHT.KG)),
>  xlab="Date",ylab="Weight (kg)",type="n")
>  lines(dates,WEIGHT.KG)
>  points(dates,WEIGHT.KG)
>
>I find that the data points are all plotted at (x-1,y),
>where x is in days.  Have I requested this behaviour
>accidentally?  I'm using R-1.8 on OS X.
>
>Printing the dates object looks correct, and simple
>manipulations such as max(dates)-min(dates) behave
>normally.
>
>Jacob Etches
>
>Doctoral candidate
>Dept of Public Health Sciences
>University of Toronto
>
>
>______________________________________________
>R-help at stat.math.ethz.ch mailing list
>https://www.stat.math.ethz.ch/mailman/listinfo/r-help


-- 
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA