title: spark: explanation of Row getDouble method
body: <p>I am using getDouble(0) where the value at index 0 is "2". My assumption was that the string would be cast to Double but I am getting a String cannot be cast to Double error. How is getDouble supposed to be used if not to cast the value at an index to Double? What is the preferred way -- <code>getString(0).toDouble</code>?</p>