On Sat, Mar 6, 2010 at 10:26 PM, Ian Mallett <geometrian@gmail.com> wrote:

On Sat, Mar 6, 2010 at 9:46 PM, David Goldsmith <d.l.goldsmith@gmail.com> wrote:

Thanks, Ian. I already figured out how to make it not so, but I still want to understand the design reasoning behind it being so in the first place (thus the use of the question "why (is it so)," not "how (to make it different)").
Well, I can't help you with that. I would also ask why this design even exists? Equating an array with a single number doesn't make sense to me.

Ian

Here's an (unintended) use case:

I wanted to convert anything in an array that's close to zero to be zero (and leave the rest as is), but I want it to be robust so that if it receives a scalar, it can work w/ that, too.

Here's my (working) code (I'm sure that once Robert sees it, he'll be able to replace it w/ a one-liner):

def convert_close(arg):
    arg = N.array(arg)
    if not arg.shape:
        arg = N.array((arg,))
    if arg.size:
        t = N.array([0 if N.allclose(temp, 0) else temp for temp in arg])
        if len(t.shape) - 1:
            return N.squeeze(t)
        else:
            return t
    else:
        return N.array()

At first I wasn't "casting" arg to be an array upon entry, but I found that if arg is a scalar, my list comprehension failed, so I had choose _some_ sort of sequence to cast scalars to; since arg will typically be an array and that's what I wanted to return as well, it seemed most appropriate to "cast" incoming scalars to arrays. So I added the arg = N.array(arg) at the beginning (N.array(array) = array, and N.array(non-array seq) does the "right" thing as well), but the list comprehension still wouldn't work if arg was a scalar upon entry; after many print statements and much interactive experimenting, I finally figured out that this is because the shape of N.array(scalar) is () (and I thence immediately guessed, correctly of course, that N.array((scalar,)) has shape (1,)). So I added the if not arg.shape: to detect and correct for those zero size arrays, and now it works fine, but I'd still like to know _why_ N.array(scalar).shape == () but N.array((scalar,)).shape == (1,). No biggy, just curious.

DG