[R] How to draw plot marks without label?

[Luigi Marongiu]

I would like to draw a graph where the y-lables are missing but the
marks still present.
In this example, I get marks from 20000 to 140 000 with increments of
20 000. I could use `plot(... yaxt="n"...)` combined with `axis(2,
at..., label="")` but this needs to know exactly the sequence of marks
provided by plot. But this sequence might change.

Thus is there a way to plot the marks without labels?
Also, is it possible to draw the marks on the right side?

Thank you.

```
y = c(42008, 19076, 150576, 48192, 26153, 37931, 36103, 17692,
      61538,41027, 71052, 94571)
df = data.frame(X = c(rep(0, 6), rep(25, 6)), Y = y)
stripchart(df$Y ~ df$X,
           method = "jitter", offset=1/3,
           vertical = TRUE, las=1,
           pch=16, cex=2,
           ylab="Y", xlab="X",
           main="Example")
```