[R] Ploting NA location points

[Trent Piepho]

> Kenneth Cabrera <krcabrer at epm.net.co> writes:
> > How can I plot a x,y coordinates, but to plot a "z" variable
> > with a different color if it is a z missing value (NA)?
> > 
> 

Also this:

plot(x,y, pch=21, bg=c(4,2)[is.na(z)+1])

You need to use a point type from 21 to 25 for the background color to show
up.  If you don't want a filled point, use col instead of bg and whatever
point type you want.  You could also do something like
"pch=c(20,1)[is.na(z)+1]", to get different point types when z is missing.

To go along with the plot, I suggest something like:

legend(0,0, c("Non-Missing", "Missing"), fill=c(4,2))

The legend will have square boxes of color instead of filled circles like
pch=21,bg=c(...) will give you.  I haven't been able to figure out how to get
a color filled symbol in a plot legend.  The bg parameter will apply to the
background of the entire legend, and not the plotting symbols.

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