title: What would be a good way to represent a vector of hierarchical objects?
body: <p>I have an object represented as nested dictionaries \ arrays
  all objects in the set have the same schema, though the number of entries in arrays may vary from object to object
  I'm looking for a good way to store this data, that will allow simple batch operations.
  specifically, fast access to a column \ set of columns as numpy arrays is important (which is the main reason not to use a simple list of objects)</p>
  
  <p>pandas with MultiIndex was my 1st idea, but I don't believe it can support variable length arrays</p>