title: How to convert R formula to text?
body: <p>I have trouble working with formula as with text. What I'm trying to do is to concatenate the formula to the title of the graph. However, when I try to work with the formula as with text, I fail:</p>
  
  <pre><code>model &lt;- lm(celkem ~ rok + mesic)
  formula(model)
  # celkem ~ rok + mesic
  </code></pre>
  
  <p>This is fine. Now I want to build string like <code>"my text celkem ~ rok + mesic"</code> - this is where the problem comes:</p>
  
  <pre><code>paste("my text", formula(model))
  # [1] "my text ~"           "my text celkem"      "my text rok + mesic"
  
  paste("my text", as.character(formula(model)))
  # [1] "my text ~"           "my text celkem"      "my text rok + mesic"
  
  paste("my text", toString(formula(model)))
  # [1] "my text ~, celkem, rok + mesic"
  </code></pre>
  
  <p>Now I see there is a <code>sprint</code> function in package <code>gtools</code>, but I think this is such a basic thing that it deserves a solution within the default environment!!</p>