> May be weird, but I think the subclass of the data is conserved, so this needs to check
> explicitly for non-masked arrays. 

@seberg - I don't understand this comment.  Are you saying that if x is a MaskedArray with mask set to nomask and data being a subclass of ndarray this subclass should be preserved?  I am not sure how this situation is possible with the current implementation of MaskedArray as a subclass of ndarray.  Can you show a test case where you think my code produces a wrong result?

I am starting to think that it is best to rewrite ma.compressed() simply as

```
def compressed(x):
      return asarray(x).compressed()
```

and leave optimization of non-masked case for the future.