title: IBrokers: reqMktData specific field
body: <p>Here's the very simple code, but you need Interactive Brokers' TWS to run it:</p>
  
  <pre><code>opt &lt;- twsOption(local = '', expiry = '20121019', 
                   strike = '146', right = 'C', symbol = 'SPY')
  reqMktData(tws, opt, verbose = FALSE)
  </code></pre>
  
  <p>Running it, you'll get a stream of SPY Oct. '12 C146 datas; my question is: how may I tell IBrokers API to return me just particular fields, like underlying price, implied volatility, Delta Greek etc. instead of that data stream?</p>
  
  <p>I would need to manage those datas in formulas etc.</p>
  
  <p>Thanks,</p>