numpy-discussion

[Numpy-discussion] numarray equality testing

[Perry G. <pe...@st...>]

This is a Numeric/numarray compatibility question.

Numeric currently allows the equals ufunc to compare 
arrays of unequal sizes and returns a scalar 0 in such
cases. When arrays have consistent shapes, an array of
ints is returned. We argue that this is inconsistent with
normal ufunc behavior and that it should generate an
exception as do all non-equality ufuncs. (numarray currently
does not allow comparison of shape-inconsistent arrays
including for equality). 

Instead we propose a function whose purpose is to determine
if two arrays are shape consistent (i.e., can be broadcast
against each other) and have all values equal to each other.

>>> array_equal(arange(2), arange(4))
0
>>> array_equal(array([1,2,3]), array([1,2,0]))
0
>>> array_equal( arange(2), None )
0
>>> array_equal( arange(2), not_an_ndarray_instance)
0
>>> array_equal(array([[1,2,3],[1,2,3]]), array([1,2,3]))
1

Comments?

Perry Greenfield

[Numpy-discussion] Re: [SciPy-user] numarray equality testing

[Pearu P. <pe...@ce...>]

On Mon, 9 Dec 2002, Perry Greenfield wrote:

> >>> array_equal(array([[1,2,3],[1,2,3]]), array([1,2,3]))
> 1

Hmm, I would have expected 0. 
What's the rationale for 1?

May be you meant

>>> array_equal(array([[1,2,3]]), array([1,2,3]))
1

which I would agree. Also

>>> array_equal(array([[1],[2],[3]]), array([1,2,3]))
1

but I am not sure about

>>> array_equal(array([[1,2,3],[1,2,3]]), array([1,2,3,1,2,3]))
1

Pearu

[Numpy-discussion] RE: numarray equality testing

[Perry G. <pe...@st...>]

Pearu Peterson write:

> On Mon, 9 Dec 2002, Perry Greenfield wrote:
> 
> > >>> array_equal(array([[1,2,3],[1,2,3]]), array([1,2,3]))
> > 1
> 
> Hmm, I would have expected 0. 
> What's the rationale for 1?
> 
Because the arrays can be broadcast into a consistent 
array. In other words

equals(array([[1,2,3],[1,2,3]]), array([1,2,3])

returns

array([[1,1,1],[1,1,1]])

But I take your meaning. There may be those that wish
to ensure that two arrays are really identical in shape
and have all equal values. Should these be two different
functions? One function with different options.
By the way, I'm open to better function names as Tim Hochberg
suggests.

> May be you meant
> 
> >>> array_equal(array([[1,2,3]]), array([1,2,3]))
> 1
> 
> which I would agree. Also
> 
> >>> array_equal(array([[1],[2],[3]]), array([1,2,3]))
> 1
> 
> but I am not sure about
> 
> >>> array_equal(array([[1,2,3],[1,2,3]]), array([1,2,3,1,2,3]))
> 1
> 
> Pearu

Perry 

Re: [Numpy-discussion] numarray equality testing

[Konrad H. <hi...@cn...>]

"Perry Greenfield" <pe...@st...> writes:

> Instead we propose a function whose purpose is to determine
> if two arrays are shape consistent (i.e., can be broadcast
> against each other) and have all values equal to each other.

So there would be that operation, plus one that checks identity
of shape and all elements? That should cover all needs I can think of.

Konrad.

[Numpy-discussion] Re: [SciPy-user] numarray equality testing

[Robert K. <ke...@ca...>]

On Mon, Dec 09, 2002 at 09:06:43AM -0700, Tim Hochberg wrote:

[snip]

> This seems like a good plan. I'm not enthralled by the name though:
> array_equal seems equally likely to describethe  behaviour of the unfunc
> equal as it does the behaviour above. Maybe array_identical or array_same or
> equal_arrays or some such (although none of those are great).

I'd put in my vote for array_equiv, equiv, or equivalent since I think
"equivalence" best expresses the relationship tested here, not
"equality."

> -tim

-- 
Robert Kern
Ruddock House President
ke...@ca...

"In the fields of hell where the grass grows high
 Are the graves of dreams allowed to die."
  -- Richard Harter