[R] ticks on the Time Axis

[Gabor Grothendieck]

Laura Holt <lauraholt_983 <at> hotmail.com> writes:

: 
: Dear R People:
: 
: I have the following montly time series
: >ya.ts
:       Jan  Feb  Mar  Apr  May  Jun  Jul  Aug  Sep  Oct  Nov  Dec
: 2001  3.7 -0.8  0.3 -1.5 -0.2 -0.4  2.5 -1.0 -1.2 -1.2  0.4 -0.5
: 2002  0.5  0.0 -0.8 -1.0  0.6  0.8 -0.5 -2.4  1.3  1.4 -0.1  0.5
: >plot(ya.ts)
: 
: When the plot is constructed, the ticks on the horizontal (time) axis are 
: 2001.0, 2001.5, and so on.
: 
: Is there a way to set up ticks such as J,F,M,A,M......by months, please?

This is not quite what you are asking for since the months are in 
numbers (Jan = 01) and it may print only every third month if its
too cramped but its easy (no messing with axes) and it may be good 
enough.  It uses the fact that the chron package will plot numeric 
months and years.

   require(chron)
   ya.start.date <- chron("1/1/1")
   ya.dates <- seq(ya.start.date, length = length(ya.ts), by = "month")
   plot(ya.dates, ya.ts)

If you want to automatically construct ya.start.date above from ya.ts,
use the fact that year-month-day character format is accepted by Date to 
get the start date as a Date, convert that to chron and then use that in 
place of the ya.start.date <- line above:

   ya.start.date <- chron(as.Date(paste(c(start(ya.ts),1), collapse="-")))