On 9/6/06, Travis Oliphant <[EMAIL PROTECTED]> wrote:
OK. I do have a couple of questions. Let me insert the docs for array and asarray :
"""array(object, dtype=None, copy=1,order=None, subok=0,ndmin=0)
Return an array from object with the specified date-type.
Inputs:
object - an array, any object exposing the array interface, any
object whose __array__ method returns an array, or any
(nested) sequence.
dtype - The desired data-type for the array. If not given, then
the type will be determined as the minimum type required
to hold the objects in the sequence. This argument can only
be used to 'upcast' the array. For downcasting, use the
.astype(t) method.
copy - If true, then force a copy. Otherwise a copy will only occur
if __array__ returns a copy, obj is a nested sequence, or
a copy is needed to satisfy any of the other requirements
order - Specify the order of the array. If order is 'C', then the
array will be in C-contiguous order (last-index varies the
fastest). If order is 'FORTRAN', then the returned array
will be in Fortran-contiguous order (first-index varies the
fastest). If order is None, then the returned array may
be in either C-, or Fortran-contiguous order or even
discontiguous.
subok - If True, then sub-classes will be passed-through, otherwise
the returned array will be forced to be a base-class array
ndmin - Specifies the minimum number of dimensions that the resulting
array should have. 1's will be pre-pended to the shape as
needed to meet this requirement.
""")
asarray(a, dtype=None, order=None)
Returns a as an array.
Unlike array(), no copy is performed if a is already an array. Subclasses
are converted to base class ndarray.
1) Is it true that array doesn't always return a copy except by default? asarray says it contrasts with array in this regard. Maybe copy=0 should be deprecated.
2) Is asarray is basically array with copy=0?
3) Is asanyarray basically array with copy=0 and subok=1?
4) Is there some sort of precedence table for conversions? To me it looks like the most deeply nested lists are converted to arrays first, numeric if they contain all numeric types, object otherwise. I assume the algorithm then ascends up through the hierarchy like traversing a binary tree in postorder?
5) All nesting must be to the same depth and the deepest nested items must have the same length.
6) How is the difference between lists and "lists" determined, i.e.,
In [3]: array([list([1,2,3]),list([1,2])], dtype = object)
Out[3]: array([[1, 2, 3], [1, 2]], dtype=object)
In [8]: array([array([1,2,3]),array([1,2])], dtype = object)
Out[8]: array([[1 2 3], [1 2]], dtype=object)
In [9]: array([1,2,3],[1,2]], dtype = object)
------------------------------------------------------------
File "<ipython console>", line 1
array([1,2,3],[1,2]], dtype = object)
^
SyntaxError: invalid syntax
Is the difference that list(...) and array(...) are passed as functions (lazy evaluation), but a list is just a list?
Sorry to be asking all these questions, but I would like to try making the documentation be a bit of a reference. I am sure I will have more questions ;)
Chuck
Charles R Harris wrote:
>
> Where is array at this point?
Basically it supports the old Numeric behavior wherein object array's
are treated as before *except* for when an error would have occurred
previously when the "new behavior" kicks in. Anything that violates
that is a bug needing to be fixed.
This leaves the new object-array constructor used less often. It could
be exported explicitly into an oarray constructor, but I'm not sure
about the advantages of that approach. There are benefits to having
object arrays constructed in the same way as other arrays. It turns out
many people actually like that feature of Numeric, which is the reason I
didn't go the route of numarray which pulled object arrays out.
At this point, however, object arrays can even be part of records and so
need to be an integral part of the data-type description. Pulling that
out is not going to happen. A more intelligent object-array
constructor, however, may be a useful tool.
OK. I do have a couple of questions. Let me insert the docs for array and asarray :
"""array(object, dtype=None, copy=1,order=None, subok=0,ndmin=0)
Return an array from object with the specified date-type.
Inputs:
object - an array, any object exposing the array interface, any
object whose __array__ method returns an array, or any
(nested) sequence.
dtype - The desired data-type for the array. If not given, then
the type will be determined as the minimum type required
to hold the objects in the sequence. This argument can only
be used to 'upcast' the array. For downcasting, use the
.astype(t) method.
copy - If true, then force a copy. Otherwise a copy will only occur
if __array__ returns a copy, obj is a nested sequence, or
a copy is needed to satisfy any of the other requirements
order - Specify the order of the array. If order is 'C', then the
array will be in C-contiguous order (last-index varies the
fastest). If order is 'FORTRAN', then the returned array
will be in Fortran-contiguous order (first-index varies the
fastest). If order is None, then the returned array may
be in either C-, or Fortran-contiguous order or even
discontiguous.
subok - If True, then sub-classes will be passed-through, otherwise
the returned array will be forced to be a base-class array
ndmin - Specifies the minimum number of dimensions that the resulting
array should have. 1's will be pre-pended to the shape as
needed to meet this requirement.
""")
asarray(a, dtype=None, order=None)
Returns a as an array.
Unlike array(), no copy is performed if a is already an array. Subclasses
are converted to base class ndarray.
1) Is it true that array doesn't always return a copy except by default? asarray says it contrasts with array in this regard. Maybe copy=0 should be deprecated.
2) Is asarray is basically array with copy=0?
3) Is asanyarray basically array with copy=0 and subok=1?
4) Is there some sort of precedence table for conversions? To me it looks like the most deeply nested lists are converted to arrays first, numeric if they contain all numeric types, object otherwise. I assume the algorithm then ascends up through the hierarchy like traversing a binary tree in postorder?
5) All nesting must be to the same depth and the deepest nested items must have the same length.
6) How is the difference between lists and "lists" determined, i.e.,
In [3]: array([list([1,2,3]),list([1,2])], dtype = object)
Out[3]: array([[1, 2, 3], [1, 2]], dtype=object)
In [8]: array([array([1,2,3]),array([1,2])], dtype = object)
Out[8]: array([[1 2 3], [1 2]], dtype=object)
In [9]: array([1,2,3],[1,2]], dtype = object)
------------------------------------------------------------
File "<ipython console>", line 1
array([1,2,3],[1,2]], dtype = object)
^
SyntaxError: invalid syntax
Is the difference that list(...) and array(...) are passed as functions (lazy evaluation), but a list is just a list?
Sorry to be asking all these questions, but I would like to try making the documentation be a bit of a reference. I am sure I will have more questions ;)
-Travis
Chuck
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