title: coplot in R - how to tell which plot is which
body: <p>I am using <code>coplot</code> in R to plot some conditioning plots:</p>
  
  <pre><code>coplot(var1 ~ var2 | var3, data=dtb, number=5, overlap=.1, panel=function(x,y, col, pch) {idx = order(x); lines(x[idx], predict(loess(y ~ x))[idx], pch = pch, col = col)})
  </code></pre>
  
  <p>How can one tell which plot corresponds to which "bucket" of the conditioning variable, in this case <code>var3</code>?</p>
  
  <pre><code>&gt; dput(dtb)
  structure(list(var1 = 1:50, var2 = c(50L, 49L, 48L, 47L, 46L, 
  45L, 44L, 43L, 42L, 41L, 40L, 39L, 38L, 37L, 36L, 35L, 34L, 33L, 
  32L, 31L, 30L, 29L, 28L, 27L, 26L, 25L, 24L, 23L, 22L, 21L, 20L, 
  19L, 18L, 17L, 16L, 15L, 14L, 13L, 12L, 11L, 10L, 9L, 8L, 7L, 
  6L, 5L, 4L, 3L, 2L, 1L), var3 = c(1L, 2L, 3L, 4L, 5L, 6L, 7L, 
  8L, 9L, 10L, 1L, 2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L, 1L, 2L, 
  3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L, 1L, 2L, 3L, 4L, 5L, 6L, 7L, 
  8L, 9L, 10L, 1L, 2L, 3L, 4L, 5L, 6L, 7L, 8L, 9L, 10L)), .Names = c("var1", 
  "var2", "var3"), row.names = c(NA, -50L), class = "data.frame")
  </code></pre>