What are the semantics of the "take" function? I would have expected that the following have the same shape and size:
a = array([1,2,3]) inds = a.nonzero() a[inds] array([1, 2, 3]) a.take(inds) array([[1, 2, 3]])
Is there a bug somewhere here or is this intentional? Michael.
Michael McNeil Forbes wrote:
What are the semantics of the "take" function?
I would have expected that the following have the same shape and size:
a = array([1,2,3]) inds = a.nonzero() a[inds] array([1, 2, 3]) a.take(inds) array([[1, 2, 3]])
Is there a bug somewhere here or is this intentional?
It's a result of a.nonzero() returning a tuple. In [3]: a.nonzero() Out[3]: (array([0, 1, 2]),) __getitem__ interprets tuples specially: a[1,2,3] == a[(1,2,3)], also a[0,] == a[0]. .take() doesn't; it simply tries to convert its argument into an array. It can convert (array([0, 1, 2]),) into array([[0, 1, 2]]), so it does. -- 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
Robert Kern <robert.kern@gmail.com> wrote:
Michael McNeil Forbes wrote:
What are the semantics of the "take" function?
I would have expected that the following have the same shape and size:
a = array([1,2,3]) inds = a.nonzero() a[inds] array([1, 2, 3]) a.take(inds) array([[1, 2, 3]])
Is there a bug somewhere here or is this intentional?
It's a result of a.nonzero() returning a tuple. ... __getitem__ interprets tuples specially: a[1,2,3] == a[(1,2,3)], also a[0,] == a[0].
.take() doesn't; it simply tries to convert its argument into an array. It can convert (array([0, 1, 2]),) into array([[0, 1, 2]]), so it does.
Okay. I understand why this happens from the code. 1) Is there a design reason for this inconsistent treatment of "indices"? 2) If so, is there some place (perhaps on the Wiki or in some source code I cannot find) that design decisions like this are discussed? (I have several other inconsistencies I would like to address, but would like to find out if they are "intentional" before wasting people's time.) Thanks, Michael.
Michael McNeil Forbes wrote:
Robert Kern <robert.kern@gmail.com> wrote:
Michael McNeil Forbes wrote:
What are the semantics of the "take" function?
I would have expected that the following have the same shape and size:
a = array([1,2,3]) inds = a.nonzero() a[inds] array([1, 2, 3]) a.take(inds) array([[1, 2, 3]])
Is there a bug somewhere here or is this intentional? It's a result of a.nonzero() returning a tuple. ... __getitem__ interprets tuples specially: a[1,2,3] == a[(1,2,3)], also a[0,] == a[0].
.take() doesn't; it simply tries to convert its argument into an array. It can convert (array([0, 1, 2]),) into array([[0, 1, 2]]), so it does.
Okay. I understand why this happens from the code.
1) Is there a design reason for this inconsistent treatment of "indices"?
Indexing needs to handle tuples of indices separately from other objects in order to support x[i, j] .take() does not support multidimensional indexing, so it shouldn't try to go through the special cases that __getitem__ does. Instead, it follows the rules that nearly every other method uses (i.e. "just turn it into an array").
2) If so, is there some place (perhaps on the Wiki or in some source code I cannot find) that design decisions like this are discussed? (I have several other inconsistencies I would like to address, but would like to find out if they are "intentional" before wasting people's time.)
If they're recorded outside of the code, _The Guide to NumPy_, or the mailing list, they're here: http://projects.scipy.org/scipy/numpy -- 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
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