[R] lattice contourplots

[ivo welch]

Dear R (3.2.0, osx) experts:  I would like to create contourplots from
irregular data frames (i.e., not a matrix on a grid).    I am getting
inconsistent results from lattice contourplot().  sometimes it works
(quartz plot on contours), sometimes it doesn't (blank plot = nada).
I have tried variations from
http://stackoverflow.com/questions/10805093/contour-plot-from-data-frame
, but I do not understand the problem here.  contourplot gives no
error messages.

an example is

    require(lattice)

    d <- data.frame( x =  (1:30 + rnorm(30)), y = (1:30 + rnorm(30)) )
    d <- within(d, z <- sin(x+y))

    quartz()
    contourplot( z ~ x * y, data = d)

am I committing an error, or is there something more robust or at
least verbose, perhaps?

help appreciated.  /iaw

----
Ivo Welch (ivo.welch at gmail.com)
http://www.ivo-welch.info/