title: Cannot concatenate more than 3 elements in an expression for ggplot2's geom_text
body: <p>I have a data frame for which I'm computing a linear model and would like to include the correlation coefficient and its significance using geom_text.</p>
  
  <pre><code>structure(list(ppno = c(1L, 1L, 1L, 10L, 10L, 10L, 2L, 2L, 2L, 
  3L, 3L, 3L, 4L, 4L, 4L, 5L, 5L, 5L, 6L, 6L, 6L, 7L, 7L, 7L, 8L, 
  8L, 8L, 9L, 9L, 9L), light.color = structure(c(1L, 2L, 3L, 1L, 
  2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 
  3L, 1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L), .Label = c("B", "IR", 
  "IR+B"), class = "factor"), session = c(2L, 1L, 3L, 2L, 3L, 1L, 
  1L, 3L, 2L, 3L, 2L, 1L, 2L, 3L, 1L, 3L, 1L, 2L, 1L, 2L, 3L, 2L, 
  1L, 3L, 1L, 3L, 2L, 3L, 2L, 1L), time = structure(c(1L, 1L, 1L, 
  1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 
  1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L), .Label = c("pre", 
  "post"), class = "factor"), pre.pri.s = c(NA, NA, NA, NA, NA, 
  NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, 
  NA, NA, NA, NA, NA, NA, NA, NA, NA), pre.pri.r = c(8L, 4L, 6L, 
  2L, 2L, 4L, 10L, 12L, 9L, 24L, 16L, 15L, 15L, 15L, 15L, 3L, 5L, 
  7L, 13L, 11L, 12L, 16L, 15L, 14L, 21L, 5L, 8L, 1L, 0L, 0L), pre.nwc = c(5L, 
  2L, 4L, 2L, 2L, 4L, 10L, 10L, 9L, 11L, 10L, 11L, 12L, 11L, 11L, 
  3L, 5L, 6L, 9L, 11L, 12L, 12L, 11L, 10L, 11L, 5L, 8L, 1L, 0L, 
  0L), pre.ppi = structure(c(3L, 2L, 2L, 1L, 1L, 2L, 2L, 3L, 2L, 
  3L, 2L, 2L, 3L, 3L, 3L, 1L, 1L, 2L, NA, 2L, 2L, 3L, 3L, 3L, 4L, 
  2L, 3L, 1L, 1L, 1L), .Label = c("1", "2", "3", "4", "NULL"), class = "factor"), 
      pre.pri.nwc = c(1.6, 2, 1.5, 1, 1, 1, 1, 1.2, 1, 2.18181818181818, 
      1.6, 1.36363636363636, 1.25, 1.36363636363636, 1.36363636363636, 
      1, 1, 1.16666666666667, 1.44444444444444, 1, 1, 1.33333333333333, 
      1.36363636363636, 1.4, 1.90909090909091, 1, 1, 1, NaN, NaN
      ), post.pri.s = c(NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, 
      NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, NA, 
      NA, NA, NA, NA, NA), post.pri.r = c(4L, 4L, 7L, 0L, 0L, 4L, 
      3L, 8L, 7L, 16L, 12L, 19L, 6L, 10L, 4L, 1L, 3L, 0L, 3L, 11L, 
      15L, 8L, 9L, 9L, 8L, 4L, 3L, 0L, 0L, 0L), post.nwc = c(4L, 
      3L, 4L, 0L, 0L, 3L, 3L, 8L, 7L, 10L, 9L, 15L, 5L, 9L, 4L, 
      1L, 3L, 0L, 3L, 8L, 13L, 8L, 9L, 9L, 8L, 4L, 3L, 0L, 0L, 
      0L), post.ppi = structure(c(2L, 2L, 3L, 1L, 1L, 1L, 1L, 2L, 
      2L, 2L, 2L, 2L, 2L, 3L, 2L, 5L, 1L, 1L, NA, 3L, 2L, 1L, 1L, 
      2L, 3L, 2L, 2L, 1L, 1L, 1L), .Label = c("1", "2", "3", "4", 
      "NULL"), class = "factor"), post.pri.nwc = c(1, 1.33333333333333, 
      1.75, NaN, NaN, 1.33333333333333, 1, 1, 1, 1.6, 1.33333333333333, 
      1.26666666666667, 1.2, 1.11111111111111, 1, 1, 1, NaN, 1, 
      1.375, 1.15384615384615, 1, 1, 1, 1, 1, 1, NaN, NaN, NaN), 
      delta.pri.r = c(4, 0.1, -1, 2, 2, 0.1, 7, 4, 2, 8, 4, -4, 
      9, 5, 11, 2, 2, 7, 10, 0.1, -3, 8, 6, 5, 13, 1, 5, 1, 0.1, 
      0.1), delta.nwc = c(1, -1, 0.1, 2, 2, 1, 7, 2, 2, 1, 1, -4, 
      7, 2, 7, 2, 2, 6, 6, 3, -1, 4, 2, 1, 3, 1, 5, 1, 0.1, 0.1
      ), delta.pri.nwc = c(-0.6, -0.666666666666667, 0.25, NaN, 
      NaN, 0.333333333333333, 0.1, -0.2, 0.1, -0.581818181818182, 
      -0.266666666666667, -0.0969696969696969, -0.05, -0.252525252525252, 
      -0.363636363636364, 0.1, 0.1, NaN, -0.444444444444444, 0.375, 
      0.153846153846154, -0.333333333333333, -0.363636363636364, 
      -0.4, -0.90909090909091, 0.1, 0.1, NaN, NaN, NaN), delta.vas = c(4.081632, 
      -43.877544, -8.163264, -2.040816, 0.510204, 9.183672, 8.163264, 
      8.163264, 11.224488, 0, -14.285712, -11.224488, 19.387752, 
      0, 26.530608, 2.040816, 10.20408, 11.224488, 42.346932, -10.20408, 
      -28.06122, 11.224488, 5.612244, 21.428568, 22.448976, 0, 
      23.469384, 0.510204, -1.020408, 0)), .Names = c("ppno", "light.color", 
  "session", "time", "pre.pri.s", "pre.pri.r", "pre.nwc", "pre.ppi", 
  "pre.pri.nwc", "post.pri.s", "post.pri.r", "post.nwc", "post.ppi", 
  "post.pri.nwc", "delta.pri.r", "delta.nwc", "delta.pri.nwc", 
  "delta.vas"), row.names = c(NA, -30L), class = "data.frame")
  </code></pre>
  
  <p>Using this code for the plot.</p>
  
  <pre><code>p &lt;- ggplot(data=mpq.vas, mapping=aes(x=delta.vas, y=delta.pri.r, 
      colour=light.color)) +
    geom_point() +
    geom_smooth(aes(group=1), method="lm", size=1, colour="black")
  #
  #  Clean up the basics.
  pp &lt;- p + geom_hline(yintercept=0, colour="grey60") + 
    geom_vline(xintercept=0, colour="grey60") +
    scale_colour_manual(name="Treatment\ncolor", values=cols) +
    scale_x_continuous(name=
      expression(paste(Delta, " VAS pain [t(0) - t(60)]")))+
    scale_y_continuous(name=expression(paste(Delta, "PRI(r) [pre - post]")))
  #
  #  Add correlation info.
  val &lt;- cor.test(mpq.vas$delta.vas, mpq.vas$delta.pri.r)
  </code></pre>
  
  <p>When I then try to add the correlation coefficient somewhere in the text, I get an <strong>error about an unexpected symbol</strong> at the location of the Q in the label.</p>
  
  <pre><code>pp + geom_text(aes(x=20, y=-5, label=paste("italic(r) ==", 3, "Q", sep=" ")), 
      parse=TRUE, colour="black")
  </code></pre>
  
  <p>(yes, I know a correlation of 3 is impossible, just an example).</p>
  
  <p>I would like to do:</p>
  
  <pre><code>pp + geom_text(aes(x=20, y=-5, label=paste("italic(r) ==", round(val$estimate, digits=2), "\np &lt; 0.0001", sep=" ")),     parse=TRUE, colour="black")
  </code></pre>
  
  <p>But this generates the same error, now at the \n thingy. What am I doing wrong?</p>