RE: [Matplotlib-users] Problem with vlines ... and tcl !!!

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

John Hunter wrote:
> 
> Now on to your problem.  This is caused by a difference in how Numeric
> and numarray treak rank 0 arrays
> 
>     >>> from Numeric import asarray
>     >>> len(asarray(0))
>     1
>     >>> from numarray import asarray
>     >>> len(asarray(0))
>     Traceback (most recent call last):
>       File "<stdin>", line 1, in ?
>     ValueError: Rank-0 array has no length.
> 
> I don't know why there is this difference but I'm sure Todd or Perry
> can comment at length :-).
> 
Boy can we (and we have on the numpy list in the past). 
But I risk boring those who really don't care. The issue relates
to consistency. If rank-0 arrays have a shape of () (and they
do), then they:

1) should not be indexable.
2) they have no length.

Currently Numeric gives len=1 and allows indexing with [0]

It's seemed to me that we need some sort of construct similar to
array() that will turn scalars into rank-1 len-1 arrays which
can be used like scalars for broadcasting purposes (albeit with
different coercion rules; that's a different topic though), and
where len() and indexing will work.

Another proposal is to treat all arrays (including rank-0) as 
allowing indexing with any number of 0 indices beyond the defined shape:
I.e., if 

x = arange(10)
x[3,0] # same as x[3]

So it's a known issue and we are thinking about how best to solve it.

> To solve your vline problem, you need to make the vmin and vmax args
> of vlines (or hlines) iterable.  Ie
> 
> old
> 
>   vlines(t, 0, s, color='k')
> 
> new
> 
>   vlines(t, [0], s, color='k')
>   
> Should work!  Thanks for letting us know.
> 
>