title: apply over matrix by column - any way to get column name?
body: <p>I'm calling <code>apply(data, 2, function(x) {...})</code> where <code>data</code> is a matrix.  Is there any way for the function to know the name of the column whose values are present in <code>x</code>?  Or perhaps there's another function to accomplish the same task?</p>