[R] Why does a date frame returning date with a time zone sometimes?

[arun]

I may have misunderstood your question.  

vec1 <- seq(as.POSIXct("2009-01-01 00:00:00",format="%Y-%m-%d %H:%M:%S"),by= '12 hour', length=12)

vec1[1:3] #returns with time zone
#[1] "2009-01-01 00:00:00 EST" "2009-01-01 12:00:00 EST"
#[3] "2009-01-02 00:00:00 EST"

If you don't want the time zone info:,
strftime(vec1,usetz=FALSE)[1:2]
#[1] "2009-01-01 00:00:00" "2009-01-01 12:00:00"


Also, you can change the time zone,



Sys.setenv(TZ="GMT")
 vec1[1:2]
#[1] "2009-01-01 05:00:00 GMT" "2009-01-01 17:00:00 GMT"

It is not clear what you want.
A.K.


I have a date from which returns 
head(mt, 3) 
                DateW             |         Date                               |tempDeg 
2 2009-01-01 01:00:00       |         2009-01-01 01:00:00        |          -23.6 
3 2009-01-01 02:00:00       |         2009-01-01 02:00:00        |          -25.7 
4 2009-01-01 03:00:00       |         2009-01-01 03:00:00        |          -26.5 


Why does this return  a time with MST? 

mt[1,2] 
[1] "2009-01-01 01:00:00 MST"