[R] types of vectors / lists

[Erik Iverson]

Hello -

a9804814 at unet.univie.ac.at wrote:
> Hello,
> 
> I am an advanced user of R. Recently I found out that apparently I do 
> not fully understand vectors and lists fully
> Take this code snippet:
> 
> 
> T = c("02.03.2008 12:23", "03.03.2008 05:54")
> Times = strptime(T, "%d.%m.%Y %H:%M")
> Times                 # OK
> class(Times)          # OK
> is.list(Times)        # sort of understand and not understand that

?POSIXlt says

Class '"POSIXlt"' is a named list of
      vectors representing

      'sec' 0-61: seconds

      'min' 0-59: minutes

      'hour' 0-23: hours

      'mday' 1-31: day of the month

      'mon' 0-11: months after the first of the year.

      'year' Years since 1900.

      'wday' 0-6 day of the week, starting on Sunday.

      'yday' 0-365: day of the year.

      'isdst' Daylight savings time flag.  Positive if in force, zero if
           not, negative if unknown.


> length(Times)         # 9 ??? why is it length(Times[1]) ??

Because Times is a list with 9 elements, try typing names(Times) to see 
what those elements are called.  That will help you understand.

> 
> Times[1] # OK
> Times[[1]] # Wrong

Whether or not this is 'wrong' has been I believe debated before on the 
list.  See this message and the rest of the thread associated with it.

http://tolstoy.newcastle.edu.au/R/help/06/07/31508.html

- Erik Iverson