Re: [Numpy-discussion] short circuit != ?
how about np.any(a!=b) ?? On 10/27/2010 12:25 PM, Neal Becker wrote: Is there a way to get a short circuit != ? That is, compare 2 arrays but stop as soon as the first element comparison fails? I'm assuming that np.all (a != b) will _not_ do this, but will first compare all elements. ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] short circuit != ?
Johann Cohen-Tanugi wrote: how about np.any(a!=b) ?? On 10/27/2010 12:25 PM, Neal Becker wrote: Is there a way to get a short circuit != ? That is, compare 2 arrays but stop as soon as the first element comparison fails? I'm assuming that np.all (a != b) will _not_ do this, but will first compare all elements. ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion I don't think that will do short ciruit, will it? I think that will compare each element, returning a bool array, then short-circuit eval that bool array. ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] short circuit != ?
On 10/27/2010 03:31 PM, Neal Becker wrote: Johann Cohen-Tanugi wrote: how about np.any(a!=b) ?? On 10/27/2010 12:25 PM, Neal Becker wrote: Is there a way to get a short circuit != ? That is, compare 2 arrays but stop as soon as the first element comparison fails? I'm assuming that np.all (a != b) will _not_ do this, but will first compare all elements. ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion I don't think that will do short ciruit, will it? I think that will compare each element, returning a bool array, then short-circuit eval that bool array. In [3]: a=np.array([2,3, In [4]: b=np.array([2,5, In [5]: np.any(a!=b) Out[5]: True it does not return a bool array, it seems. I do not see how you would broadcast the notion of any along axes maybe? ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] short circuit != ?
On Wed, Oct 27, 2010 at 9:37 AM, Johann Cohen-Tanugi co...@lpta.in2p3.fr wrote: On 10/27/2010 03:31 PM, Neal Becker wrote: Johann Cohen-Tanugi wrote: how about np.any(a!=b) ?? On 10/27/2010 12:25 PM, Neal Becker wrote: Is there a way to get a short circuit != ? That is, compare 2 arrays but stop as soon as the first element comparison fails? I'm assuming that np.all (a != b) will _not_ do this, but will first compare all elements. ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion I don't think that will do short ciruit, will it? I think that will compare each element, returning a bool array, then short-circuit eval that bool array. In [3]: a=np.array([2,3, In [4]: b=np.array([2,5, In [5]: np.any(a!=b) Out[5]: True it does not return a bool array, it seems. I do not see how you would broadcast the notion of any along axes maybe? Not definitive by any means, but In [28]: a = np.arange(1,1000) In [29]: b = np.arange(1,1000) In [30]: timeit np.any(a!=b) 10 loops, best of 3: 37.8 ms per loop In [31]: a[0] = 10. In [32]: timeit np.any(a!=b) 10 loops, best of 3: 24.7 ms per loop In [33]: a[0] = 1 In [34]: a[-1] = 1 In [35]: timeit np.any(a!=b) 10 loops, best of 3: 37.7 ms per loop It seems to at least take less time when the difference is at the beginning, though I'm sure there could be exceptions. Skipper ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] short circuit != ?
Wed, 27 Oct 2010 09:44:59 -0400, Skipper Seabold wrote: [clip] In [35]: timeit np.any(a!=b) [clip] It seems to at least take less time when the difference is at the beginning, though I'm sure there could be exceptions. It performs all the comparisons to create a temporary boolean array. any() does return when it sees the first True, but this is not full short-circuiting. -- Pauli Virtanen ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] short circuit != ?
This is silly: the structure of the python language prevents meaningful short-circuiting in the case of np.any(a!=b) While it's true that np.any itself may short-circuit, the 'a!=b' statement itself will be evaluated in its entirety before the result (a boolean array) is passed to np.any. This is just how python (like most other languages) works. This means that the big-O complexity isn't reduced any: all elements of a and b have to be examined. If any short-circuits, then at least all the elements don't need to be examined twice! If performance actually matters here (unlikely?), a quick bit of cython code could do this easily enough in the simple case where a and b are the same shape (so no broadcasting required). Note that the below hard-codes the dtype also. import cython cimport numpy import numpy TYPE_T = numpy.int64_t TYPE = numpy.int64 @cython.boundscheck(False) def equal(a, b): cdef: numpy.ndarray[TYPE, ndim=1, negative_indices=False] a_flat = a.astype(TYPE).flatten() numpy.ndarray[TYPE, ndim=1, negative_indices=False] b_flat = b.astype(TYPE).flatten() unsigned int i, l assert a_flat.shape[0] == b_flat.shape[0] l = a_flat.shape[0] for i in range(l): if a_flat[i] != b_flat[i]: return False return True Zach On Oct 27, 2010, at 9:44 AM, Skipper Seabold wrote: On Wed, Oct 27, 2010 at 9:37 AM, Johann Cohen-Tanugi co...@lpta.in2p3.fr wrote: On 10/27/2010 03:31 PM, Neal Becker wrote: Johann Cohen-Tanugi wrote: how about np.any(a!=b) ?? On 10/27/2010 12:25 PM, Neal Becker wrote: Is there a way to get a short circuit != ? That is, compare 2 arrays but stop as soon as the first element comparison fails? I'm assuming that np.all (a != b) will _not_ do this, but will first compare all elements. ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion I don't think that will do short ciruit, will it? I think that will compare each element, returning a bool array, then short-circuit eval that bool array. In [3]: a=np.array([2,3, In [4]: b=np.array([2,5, In [5]: np.any(a!=b) Out[5]: True it does not return a bool array, it seems. I do not see how you would broadcast the notion of any along axes maybe? Not definitive by any means, but In [28]: a = np.arange(1,1000) In [29]: b = np.arange(1,1000) In [30]: timeit np.any(a!=b) 10 loops, best of 3: 37.8 ms per loop In [31]: a[0] = 10. In [32]: timeit np.any(a!=b) 10 loops, best of 3: 24.7 ms per loop In [33]: a[0] = 1 In [34]: a[-1] = 1 In [35]: timeit np.any(a!=b) 10 loops, best of 3: 37.7 ms per loop It seems to at least take less time when the difference is at the beginning, though I'm sure there could be exceptions. Skipper ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] short circuit != ?
On 10/27/2010 9:56 AM, Zachary Pincus wrote: the structure of the python language prevents meaningful short-circuiting in the case of np.any(a!=b) Maybe: any((ai != bi) for ai,bi in izip(a.flat,b.flat)) ? fwiw, Alan Isaac ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] short circuit != ?
Pauli Virtanen wrote: Wed, 27 Oct 2010 09:44:59 -0400, Skipper Seabold wrote: [clip] In [35]: timeit np.any(a!=b) [clip] It seems to at least take less time when the difference is at the beginning, though I'm sure there could be exceptions. It performs all the comparisons to create a temporary boolean array. any() does return when it sees the first True, but this is not full short-circuiting. I propose adding is_equal(a,b) function which does true short-ciruciting ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
Re: [Numpy-discussion] short circuit != ?
On Wed, Oct 27, 2010 at 7:34 AM, Neal Becker ndbeck...@gmail.com wrote: I propose adding is_equal(a,b) function which does true short-ciruciting You could use np.allclose, I guess. (It isn't short-circuiting right now, but you could fix that.) -- Nathaniel ___ NumPy-Discussion mailing list NumPy-Discussion@scipy.org http://mail.scipy.org/mailman/listinfo/numpy-discussion
