title: "Error in parse(text = x)" when running for-loop with ggplot2
body: <p>I'm trying to run a for-loop that produces plots with column names as the x label. This should be straightforward, but R's having an issue parsing the column names since they have parentheses and spaces in them, which I'd like to keep for the plot as they are descriptive author names.</p>
  
  <p>Here are the names of the columns.</p>
  
  <pre><code>colnames(shorty_ks)[colnames(shorty_ks)=="K.mean.hr"] &lt;- "BASEmetab"
  colnames(shorty_ks)[colnames(shorty_ks)=="kn2o.Churchill"] &lt;- "Churchill et al. (1962)"
  colnames(shorty_ks)[colnames(shorty_ks)=="kn2o.Owens"] &lt;- "Owens (1964)"
  colnames(shorty_ks)[colnames(shorty_ks)=="kn2o.Oconnor"] &lt;- "OConnor and Dobbins (1958)"
  </code></pre>
  
  <p>Here's the for loop (that works when I use simple text excluding spaces and parentheses):</p>
  
  <pre><code>colNames &lt;- names(shorty_ks)[2:4]
  BASEmetab &lt;- shorty_ks$BASEmetab
  
  
  for(i in colNames){
    plt &lt;- ggplot(shorty_ks, aes_string(x=i, y = BASEmetab)) + xlab(bquote(. (i)~k~(h^-1)))+ ylab(expression(BASEmetab~k~(h^-1)))+
  theme_gray()+
  geom_smooth(method="lm",se=FALSE) + geom_point() +
  scale_color_brewer(palette="Dark2")
  print(plt)
  Sys.sleep(2)
  }
  </code></pre>
  
  <p>But when I run the code with the parentheses and spaces, I get this error message:</p>
  
  <pre><code>Error in parse(text = x) : &lt;text&gt;:1:11: unexpected symbol
  1: Churchill et
                ^
  </code></pre>
  
  <p>Reproducible data:</p>
  
  <pre><code>dput(head(shorty_ks))
  structure(list(BASEmetab = c(0.11409531425, 0.0716102175833333, 
  0.09953587425, 0.248902252416667, 0.114263822125, 0.1530849725
  ), `Churchill et al. (1962)` = c(0.0354781748244595, 0.0511254328535874, 
  0.0351401193406382, 0.0432339955562482, 0.0498228392372491, 
  0.0342448057447306
  ), `OConnor and Dobbins (1958)` = c(0.0336761898724322, 0.0447691111499001, 
  0.0333255117582665, 0.0359191513743014, 0.043530785730249, 0.0324037193153706
  ), `Owens (1964)` = c(0.0585830015888074, 0.10004459351892, 
  0.0583011578948275, 
  0.102948639254916, 0.0987018589393615, 0.0575186770232462)), .Names = 
  c("BASEmetab", 
  "Churchill et al. (1962)", "OConnor and Dobbins (1958)", "Owens (1964)"
  ), row.names = c(NA, 6L), class = "data.frame")
  </code></pre>