[yt-dev] Boolean data objects in yt-3

[Matthew Turk]

Hi,

I don't have time to do this right now, but here is how I would
implement boolean objects.

 * Implement a new binary operation subclass selector which always has
two cdef'd selector objects as attributes.  *No* unary operations;
these should be implemented as binary with AlwaysSelector.
 * Subclass that with the necessary binary boolean operations (and, or, xor)
 * Implement all subclassed selection operations with wrappers around
calling each individual selector's operations
 * Exclusively chain these operations in python using the built-in AST
by implementing dunder logic operations
 * Do not at any time implement a DSL
 * If necessary, implement a union operator that accepts multiple
selector objects

-Matt

On Fri, Jun 10, 2016 at 9:11 AM, Brian O'Shea <bwoshea at gmail.com> wrote:
>>>>> I've stumbled across across a research task that could really use yt's
>>>>> Boolean data object feature, and according to the documentation it is not
>>>>> implemented in yt-3.  Have boolean data objects been replaced by something
>>>>> else?  I know there are various filtering methods in yt, but what I really
>>>>> need to do is spatial filtering (i.e., data in a sphere with some chunks of
>>>>> the sphere excised).
>>>>
>>>>
>>>> This hasn't been implemented.
>>>>
>>>>>
>>>>>
>>>>> In principle I'd be happy to take a crack at re-implementing it,
>>>>> although I might need some help.  Could somebody give me a sense of why it
>>>>> wasn't ported to yt-3 when the changeover was made?
>>>>
>>>>
>>>> The data selection API was completely rewritten.
>>>
>>>
>>> How difficult might it be to re-implement the boolean data objects in the
>>> new data selection API?  (I suppose the question is really "how difficult
>>> might it be for somebody who is a decent programmer but not an expert in
>>> yt's internals to do so"?)
>>
>>
>> I'm not sure, offhand. Probably very hard if you want to use the
>> eval-style way of contrusting the data objects using a string written in
>> Python, since data selection happens at a lower level in yt now. See
>> selection_routines.pyx for more details about how this works.
>>
>> It is possible to combine data objects by chaining data_source keyword
>> arguments, (e.g. one can create a half-sphere data object by chaining a
>> region that selects only half a sphere with a sphere data object). It may be
>> possible to generalize that somehow.
>
>
> OK, this is useful.  I will think about it a bit.  Thanks!
>
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