title: Set linetype for geom_vline?
body: <p>For the following plot:</p>
  
  <pre><code>df.plot &lt;-structure(list(color = structure(c(2L, 2L, 3L, 1L, 3L, 4L, 3L, 
      1L, 4L, 1L, 2L, 4L, 1L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 3L, 2L, 
      3L, 3L, 3L, 3L), .Label = c("54", "55", "61", "69"), class = "factor"), 
      date = structure(c(16687, 16687, 16687, 16687, 16687, 16687, 
      16688, 16688, 16688, 16689, 16689, 16690, 16693, 16693, 16693, 
      16694, 16694, 16695, 16695, 16695, 16695, 16696, 16696, 16696, 
      16696, 16696, 16696), class = "Date"), facet = c("A", 
       "A", "A", "A", "A", "B", 
       "B", "A", "B", "B", "B", "B", 
       "B", "B", "B", "B", "A", "B", 
       "A", "B", "A", "C", "B", "C", 
       "C", "B", "C")), class = "data.frame", row.names = c(NA, -27L), 
       .Names = c("color", "date", "facet"))
  
  vlines &lt;- data.frame(date = as.Date(c("2015-09-10", "2015-09-13")), 
            LType=(c("AA", "AB")))
  ggplot(df.plot, aes(x=date, fill=color)) + 
    geom_dotplot(binwidth=1, stackgroups=TRUE, binpositions="all") +
    coord_fixed(ratio=1) + 
    ylim(0,7) +
    geom_vline(data=vlines, aes(xintercept = as.numeric(date), linetype=LType))  + 
    facet_grid(facet ~ .)
  </code></pre>
  
  <p>I would like to make the line type for "AB" be "dotdash" , and for "AA" "longdash". How can I specify that?</p>