Re: [Numpy-discussion] how to create an array of objects that are sequences?
Robert Kern wrote: Chris Barker wrote: What if your objects were nested sequences, and you wanted to partly flatten them -- which would you flatten? I'm pretty sure that that is exactly the ambiguity that the depth option resolves. Can you give me an example where it's still ambiguous with the depth information provided? I was imagining: Say you have a bunch of nested sequences that, fully expanded, would yield a (i,j,k) rank-3 array. If you wanted a rank-2 array, you could have either: a (i,j) array with each element being a length-k sequence or: a (i,k) array, with each element being a length-j sequence. This is quite trivial with numpy n-d arrays. However, while you could build either of those from nested sequences, there isn't, in fact, and object in there that is that length-j sequence. I guess this really points to the power of n-d arrays! Here's a simple example: t = (((1,2),(3,4)),((5,6),(7,8))) depth 1 -- (4,): array([(1, 2), (3, 4), (5, 6), (7, 8)], dtype=object) a[0] (1, 2) depth 1 -- (2,) a array([(1, 2, 3, 4), (5, 6, 7, 8)], dtype=object) a[0] (1, 2, 3, 4) But since there was no object in the original sequence that actually had a 4-tuple, maybe no one would ever be looking for that. -Chris -- Christopher Barker, Ph.D. Oceanographer Emergency Response Division NOAA/NOS/ORR(206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception [EMAIL PROTECTED] ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] how to create an array of objects that are sequences?
Christopher Barker wrote: Robert Kern wrote: Chris Barker wrote: What if your objects were nested sequences, and you wanted to partly flatten them -- which would you flatten? I'm pretty sure that that is exactly the ambiguity that the depth option resolves. Can you give me an example where it's still ambiguous with the depth information provided? I was imagining: Say you have a bunch of nested sequences that, fully expanded, would yield a (i,j,k) rank-3 array. If you wanted a rank-2 array, you could have either: a (i,j) array with each element being a length-k sequence or: a (i,k) array, with each element being a length-j sequence. This is quite trivial with numpy n-d arrays. However, while you could build either of those from nested sequences, there isn't, in fact, and object in there that is that length-j sequence. And I think that's the key difference. I don't think array() should be responsible for *arbitrarily* flattening nested sequences in order to reinterpret structure. Instead, I think we really only need array() to be able to answer the question, is this object an atom or a sequence I need to descend into? Essentially, for all valid index-tuples (say, [i,j,k]) in the array: arr[i,j,k] == original[i,j,k] I guess this really points to the power of n-d arrays! Yes. Since one can get the (i,k) array after getting the (i,j,k) array and reshaping, I don't think we need to support it in array(). -- Robert Kern I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth. -- Umberto Eco ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] how to create an array of objects that are sequences?
On Fri, January 4, 2008 8:00 pm, Pearu Peterson wrote: On Fri, January 4, 2008 7:33 pm, Travis E. Oliphant wrote: Pearu Peterson wrote: Hi, Say, one defines class A(tuple): def __repr__(self): return 'A(%s)' % (tuple.__repr__(self)) and I'd like to create an array of A instances. So, create an empty object array and insert the entries the way you want them: a = np.empty(1,dtype=object) a[0] = A((1,2)) Meantime I was reading arrayobject.c and it seems that before objects are checked for being sequences, their __array_interface__ is accessed (eg in Array_FromSequence, discover_depth). Would this provide a solution if the class A would define a property __array_interface__? I just don't know what the data field should be for an object. Ok, I found a partial solution: class A(tuple): def __repr__(self): return 'A(%s)' % (tuple.__repr__(self)) @property def __array_interface__(self): import numpy obj = numpy.empty(1,dtype=object) obj[0] = self return obj.__array_interface__.copy() ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] how to create an array of objects that are sequences?
On Fri, January 4, 2008 8:00 pm, Pearu Peterson wrote:
On Fri, January 4, 2008 7:33 pm, Travis E. Oliphant wrote:
Pearu Peterson wrote:
Hi,
Say, one defines
class A(tuple):
def __repr__(self):
return 'A(%s)' % (tuple.__repr__(self))
and I'd like to create an array of A instances.
The array function was designed a long time ago to inspect sequences and
flatten them.
Arguably, there should be more intelligence when an object array is
requested, but there is ambiguity about what the right thing to do is.
Thus, the current situation is that if you are creating object arrays,
the advice is to populate it after the fact.
So, create an empty object array and insert the entries the way you want
them:
a = np.empty(1,dtype=object)
a[0] = A((1,2))
Meantime I was reading arrayobject.c and it seems that
before objects are checked for being sequences, their
__array_interface__ is accessed (eg in Array_FromSequence,
discover_depth).
Would this provide a solution if the class A would define
a property __array_interface__? I just don't know what
the data field should be for an object.
Ok, I found a partial solution:
class A(tuple):
def __repr__(self):
return 'A('+tuple.__repr__(self)+')'
@property
def __array_interface__(self):
import numpy
obj = numpy.empty(1,dtype=object)
obj[0] = self
return obj.__array_interface__.copy()
from numpy import *
array([A((1,2))])
array([[1, 2]], dtype=object)
but
array(A((1,2)))
array([None], dtype=object)
Pearu
PS: sorry about previous mail, Send was pressed accidentaly.
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Re: [Numpy-discussion] how to create an array of objects that are sequences?
Charles R Harris wrote: On Jan 4, 2008 11:13 AM, Pearu Peterson [EMAIL PROTECTED] mailto:[EMAIL PROTECTED] wrote: On Fri, January 4, 2008 7:33 pm, Travis E. Oliphant wrote: So, create an empty object array and insert the entries the way you want them: a = np.empty(1,dtype=object) a[0] = A((1,2)) Actually this is still an option if to put the above to a A.as_array method something like class A(tuple): def as_array(self): import numpy obj = numpy.empty(1,dtype=object) obj[0] = self return obj but it would be nice if the __array__ method also worked. Could this be something that should be put to issues or would it just get a WontFix flag? IIRC the previous discussions, there simply isn't enough information in the array interface to decide what needs to be done with regards to object arrays. I think a general solution would require a specialized creation function with more arguments, say, a depth argument which would create objects at a certain depth of nesting. In your case that would be at level 0(1?). I think that would solve most problems, and I suppose it could be added to the current array interface with a default value implying current behavior, i.e., as deep as possible. I like the depth option, and that could be used with the current interface without too much difficulty, I think. This question does come up quite often and should probably be addressed. -Travis ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] how to create an array of objects that are sequences?
Just ignore this solution. It was not quite working and I was able to get a segfault from it. Pearu On Fri, January 4, 2008 8:58 pm, Pearu Peterson wrote: On Fri, January 4, 2008 8:00 pm, Pearu Peterson wrote: On Fri, January 4, 2008 7:33 pm, Travis E. Oliphant wrote: Pearu Peterson wrote: Hi, Say, one defines class A(tuple): def __repr__(self): return 'A(%s)' % (tuple.__repr__(self)) and I'd like to create an array of A instances. So, create an empty object array and insert the entries the way you want them: a = np.empty(1,dtype=object) a[0] = A((1,2)) Meantime I was reading arrayobject.c and it seems that before objects are checked for being sequences, their __array_interface__ is accessed (eg in Array_FromSequence, discover_depth). Would this provide a solution if the class A would define a property __array_interface__? I just don't know what the data field should be for an object. Ok, I found a partial solution: class A(tuple): def __repr__(self): return 'A(%s)' % (tuple.__repr__(self)) @property def __array_interface__(self): import numpy obj = numpy.empty(1,dtype=object) obj[0] = self return obj.__array_interface__.copy() ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] how to create an array of objects that are sequences?
Travis E. Oliphant wrote: I like the depth option, and that could be used with the current interface without too much difficulty, I think. This question does come up quite often and should probably be addressed. Yes, it has, but the depth option was discussed too, and while it might solve some problems, it would still be ambiguous: What if your objects were nested sequences, and you wanted to partly flatten them -- which would you flatten? Maybe that's a weird enough case that the depth option would work most of the time, but I'm not sure. I think a shape option might cover this better. It seems the case at hand is how to make a custom object that can tell numpy how it should be put into an object array -- that may be an even rarer use case, but it seems like a good idea to support it. -Chris -- Christopher Barker, Ph.D. Oceanographer Emergency Response Division NOAA/NOS/ORR(206) 526-6959 voice 7600 Sand Point Way NE (206) 526-6329 fax Seattle, WA 98115 (206) 526-6317 main reception [EMAIL PROTECTED] ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] how to create an array of objects that are sequences?
Chris Barker wrote: Travis E. Oliphant wrote: I like the depth option, and that could be used with the current interface without too much difficulty, I think. This question does come up quite often and should probably be addressed. Yes, it has, but the depth option was discussed too, and while it might solve some problems, it would still be ambiguous: What if your objects were nested sequences, and you wanted to partly flatten them -- which would you flatten? I'm pretty sure that that is exactly the ambiguity that the depth option resolves. Can you give me an example where it's still ambiguous with the depth information provided? -- Robert Kern I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth. -- Umberto Eco ___ Numpy-discussion mailing list Numpy-discussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpy-discussion
