Hi Greg,
By default, the "axis" function puts the labels on one line and drops
labels that would overlap. When you have labels that are all the same
length, this usually results in every second, or third, or fourth
label being displayed. So you can probably get what you want by not
using staxlab. However, if you really want to use staxlab, try this:
oddones<-seq(1,length(x_yyyymmdd)-1,by=2)
staxlab(1,at=x_yyyymmdd[oddones],
labels=format(x_yyyymmdd,"%Y-%m-%d")[oddones])
It will also work with plain "axis", which is what you seem to want.
Jim