A colleague of mine just asked for help with a pesky bug that turned out to be caused by his use of a list of booleans rather than an array of booleans as his logical indexing mask. I assume this is a feature and not a bug, but it certainly surprised him: In [58]: mask = [True, False, False, False, True] In [59]: maska = n.array(mask, n.bool) In [60]: x = arange(5) In [61]: x[mask] Out[61]: array([1, 0, 0, 0, 1]) In [62]: x[maska] Out[62]: array([0, 4])
Mmm...
It looks as it 'mask' is being inernally converted from
[True, False, False, False, True]
to
[1, 0, 0, 0, 1]
so your are finally getting
x[1], x[0], x[0], x[0], x[1]
On 11/5/07, John Hunter
A colleague of mine just asked for help with a pesky bug that turned out to be caused by his use of a list of booleans rather than an array of booleans as his logical indexing mask. I assume this is a feature and not a bug, but it certainly surprised him:
In [58]: mask = [True, False, False, False, True]
In [59]: maska = n.array(mask, n.bool)
In [60]: x = arange(5)
In [61]: x[mask] Out[61]: array([1, 0, 0, 0, 1])
In [62]: x[maska] Out[62]: array([0, 4]) _______________________________________________ Numpydiscussion mailing list Numpydiscussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpydiscussion
 Lisandro Dalcín  Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC) Instituto de Desarrollo Tecnológico para la Industria Química (INTEC) Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) PTLC  Güemes 3450, (3000) Santa Fe, Argentina Tel/Fax: +54(0)342451.1594
On Nov 6, 2007 8:22 AM, Lisandro Dalcin
Mmm... It looks as it 'mask' is being inernally converted from [True, False, False, False, True] to [1, 0, 0, 0, 1]
Yep, clearly. The question is: is this the desired behavior because it leads to a "silent failure" for people who are expecting sequences of booleans to behave like arrays of booleans. JDH
On Nov 6, 2007 7:22 AM, Lisandro Dalcin
Mmm... It looks as it 'mask' is being inernally converted from [True, False, False, False, True] to [1, 0, 0, 0, 1]
so your are finally getting
x[1], x[0], x[0], x[0], x[1]
That would be my guess as well. And, it looks wrong to me. Given that array(mask) gives you the boolean mask, there's every expectation to expect the the list and array cases should be the same. I would file a bug report.
On 11/5/07, John Hunter
wrote: A colleague of mine just asked for help with a pesky bug that turned out to be caused by his use of a list of booleans rather than an array of booleans as his logical indexing mask. I assume this is a feature and not a bug, but it certainly surprised him:
In [58]: mask = [True, False, False, False, True]
In [59]: maska = n.array(mask, n.bool)
In [60]: x = arange(5)
In [61]: x[mask] Out[61]: array([1, 0, 0, 0, 1])
In [62]: x[maska] Out[62]: array([0, 4]) _______________________________________________ Numpydiscussion mailing list Numpydiscussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpydiscussion
 Lisandro Dalcín  Centro Internacional de Métodos Computacionales en Ingeniería (CIMEC) Instituto de Desarrollo Tecnológico para la Industria Química (INTEC) Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) PTLC  Güemes 3450, (3000) Santa Fe, Argentina Tel/Fax: +54(0)342451.1594 _______________________________________________ Numpydiscussion mailing list Numpydiscussion@scipy.org http://projects.scipy.org/mailman/listinfo/numpydiscussion
 . __ . \ . . tim.hochberg@ieee.org
John Hunter wrote:
A colleague of mine just asked for help with a pesky bug that turned out to be caused by his use of a list of booleans rather than an array of booleans as his logical indexing mask. I assume this is a feature and not a bug, but it certainly surprised him:
In [58]: mask = [True, False, False, False, True]
In [59]: maska = n.array(mask, n.bool)
In [60]: x = arange(5)
In [61]: x[mask] Out[61]: array([1, 0, 0, 0, 1])
In [62]: x[maska] Out[62]: array([0, 4])
The issues is how to determine what behavior is desired and how to manage that with all the possibilities. Right now the rule is that only boolean arrays are treated as masks and integer arrays mean indexing. Lists are always interpreted as integer indexing (except in certain special cases where the list has slice objects in it). Changing this to something like: lists are interpreted either as boolean or integer arrays, may be reasonable, but I don't see how we can change it until 1.1 because the rule has already been specified and is consistent if not obvious in this simple case. The question is: is anybody using boolean lists specifically according to the rule in place now? Travis
participants (4)

John Hunter

Lisandro Dalcin

Timothy Hochberg

Travis E. Oliphant