[Numpy-discussion] MA bug or feature?

Pierre GM pgmdevlist at mailcan.com
Wed Jun 21 05:12:09 CDT 2006

On Wednesday 21 June 2006 04:46, Michael Sorich wrote:
> When transposing a masked array of dtype '<f8' I noticed that an
> ndarray of dtype '|O4' was returned.

OK, I see where the problem is:
When your fill_value has a type that cannot be converted to the type of your 
data, the `filled` method (used internally in many functions, such as 
`transpose`) raises a TypeError, which is caught and your array is converted 
to 'O'.

That's what happen here: your fill_value is a string, your data are integer, 
the types don't match, hence the conversion. So, no, I don't think that's a 

Why filling when you don't have any masked values, then ? Well, there's a 
subtle difference between a boolean mask and a mask of booleans. 
When the mask is boolean (mask=nomask=False), there's no masked value, and 
`filled` returns the data.
Now, when your mask is an array of boolean (your first case), MA doesn't check 
whether mask.any()==False to determine whether there are some missing data or 
not, it just processes the whole array of boolean. 

I agree that's a bit confusing here, and there might be some room for 
improvement (for example, changing the current
`if m is nomask` to `if m is nomask or m.any()==False`, or better, forcing 
mask to nomask if mask.any()==False). But I don;t think that qualifies as 

In short:
when you have an array of numbers, don't try to fill it with characters.

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