code: def to_array(self, fields=None, axis=0):
          
          if fields is None:
              fields = self.fieldnames
          if isinstance(fields, string_types):
              fields = [fields]
          return numpy.stack([self[f] for f in fields], axis=axis)
docs: Returns an `numpy.ndarray` of self in which the fields are included
          as an extra dimension.
  
          Parameters
          ----------
          fields : {None, (list of) strings}
              The fields to get. All of the fields must have the same datatype.
              If None, will try to return all of the fields.
          axis : {0, int}
              Which dimension to put the fields in in the returned array. For
              example, if `self` has shape `(l,m,n)` and `k` fields, the
              returned array will have shape `(k,l,m,n)` if `axis=0`, `(l,k,m,n)`
              if `axis=1`, etc. Setting `axis=-1` will put the fields in the
              last dimension. Default is 0.
  
          Returns
          -------
          numpy.ndarray
              The desired fields as a numpy array.