title: main=paste( substitute(...), substitute(...) ) in R_hist_title
body: <p>I'm trying to assemble a title for a histogram plot in R. The title I want derives from two sources, first a vector (death.cause) specifying, er, cause-of-death, and second a field from a data.frame, into which I index using a list, deathratecols, to get at the field.</p>
  
  <pre><code>&gt; death.cause 
  
  &gt; [[1]] [1] "Heart Attack"
  &gt; 
  &gt; [[2]] [1] "Heart Failure"
  &gt; 
  &gt; [[3]] [1] "Pneumonia"
  
  
  &gt; deathratecols
  
  &gt; [1] 11 17 23
  </code></pre>
  
  <p>I want to assemble title like: Heart Attack (x-bar = 7.63763) , where x-bar is the mean of the data column. I can get the two parts to work separately as below. </p>
  
  <pre><code>&gt; main=substitute(x, list(x=death.cause[[i]]) )) # gives title "Heart Attack" 
  
  &gt; main=substitute(bar(X)==k, list(k=mean(outcome[, deathratecols[i] ], na.rm=TRUE   ) )) # gives title x-bar=7.63763
  </code></pre>
  
  <p>But my efforts to put the two together using paste() have failed.</p>
  
  <p>? someone point out the error of my ways please</p>