title: R: "Unary operator error" from multiline ggplot2 command
body: <p>I'm using ggplot2 to do a boxplot comparison of two different species, as indicated by the third column shown below:</p>
  
  <pre><code>&gt; library(reshape2)
  &gt; library(ggplot2)
  &gt; melt.data = melt(actb.raw.data)
  
  &gt; head(actb.raw.data)
    region  expression species
  1     CG -0.17686667   human
  2     CG -0.06506667   human
  3     DG  1.04590000   human
  4    CA1  1.94093333   human
  5    CA2  1.55023333   human
  6    CA3  1.75800000   human
  
  &gt; head(melt.data)
    region species   variable       value
  1     CG   human expression -0.17686667
  2     CG   human expression -0.06506667
  3     DG   human expression  1.04590000
  4    CA1   human expression  1.94093333
  5    CA2   human expression  1.55023333
  6    CA3   human expression  1.75800000
  </code></pre>
  
  <p>However, when I run the following code:</p>
  
  <pre><code>ggplot(combined.data, aes(x = region, y = expression, fill = species)) +
  +     geom_boxplot() +
  +     scale_fill_manual(values = c("yellow", "orange"))
  +     ggtitle("Expression comparisons for ACTB")
  +     theme(axis.text.x = element_text(angle=90, face="bold", colour="black"))
  </code></pre>
  
  <p>I get this error: </p>
  
  <pre><code>&gt; ggplot(actb.raw.data, aes(x = region, y = expression, fill = species)) +
  +     + geom_boxplot() +
  +     + scale_fill_manual(values = c("yellow", "orange"))
  Error in +geom_boxplot() : invalid argument to unary operator
  &gt; + ggtitle("ACTB expression in human vs. macaque")
  Error in +ggtitle("ACTB expression in human vs. macaque") : 
   invalid argument to unary operator
  &gt; + theme(axis.text.x = element_text(angle=90, face="bold", colour="black"))
  Error in inherits(x, "theme") : argument "e2" is missing, with no default
  </code></pre>
  
  <p>This also happens when I run using the variable melt.data, for whatever that's worth. Can someone help me fix this? I've run this code successfully before with a different dataset that was formatted identically, and I can't figure out what's going wrong here. </p>