title: R how to output "\" in sprintf
body: <p>I want to <code>sprintf</code> a  string with a <code>"\"</code> in it but it doesn't work:</p>
  
  <pre><code>sprintf("&amp; $\pm %s \delta$", 1.23)
  Error: '\p' is an unrecognized escape in character string starting ""&amp; $\p"
  </code></pre>
  
  <p>I have tried:</p>
  
  <pre><code>sprintf("&amp; $\\pm %s \\delta$", 1.23)
  [1] "&amp; $\\pm 1.23 \\delta$"
  </code></pre>
  
  <p>But I need the result with <code>"&amp; $\pm 1.23 \delta"</code></p>
  
  <p>How can I get the right result?</p>