title: sprintf format strings: reference by name?
body: <p>In Python, you can specify string formats by name (this is of course a silly example):</p>
  
  <pre><code>parameters = {'label':'months', 'april':4,'may':5,'june':6}
  formatstring = '%(label)s: %(april)d %(may)d %(june)d'
  outputstring = formatstring % parameters
  </code></pre>
  
  <p>(The <code>formatstring % parameters</code> notation is the Python equivalent to <code>do.call(sprintf,c(formatstring,as.list(parameters)))</code> in R.)</p>
  
  <p>The output string would be "<code>months: 4, 5, 6</code>". parameters is stored as a key-value pair (which might be called a dictionary, hashtable, or named list in various languages). The string format <code>%(text)s</code> allows you to reference which dictionary item (<code>text</code>) should be formatted in that slot. </p>
  
  <p>Is there anything equivalent in R, or you have you found a good workaround?</p>