Degenerate arrays get all dimensions squeeze()d out

[pao]

This shouldn't come up as much now with the changes made to the treatment of singleton dimensions, but using squeeze() on a single-element array leaves you with a zero-dimensional array which interacts with scalars, rather than with arrays:

julia> degen = squeeze([1])
0-dimensional Int64 Array:
1

julia> size(degen)
()

julia> degen*[1]
no method *(Array{Int64,0},Array{Int64,1})
 in method_missing at /home/patrick/julia/jl/base.jl:60

julia> degen*1
0-dimensional Int64 Array:
1

Would it be better to leave such single-element arrays one-dimensional, or should the singular dimension rules extend to zero-dim arrays? (Or none of the above?)

[StefanKarpinski]

I dunno. This seems like the only consistent possible behavior to me.

[JeffBezanson]

The 0-d array actually works:

julia> degen = squeeze([1])
0-dimensional Int64 Array:
1

julia> degen.*[1]
[1]

julia> degen+[1]
[2]

It works with .* and +. The problem above is that matrix multiply isn't defined for 0-d * 1-d. 1-d * 1-d doesn't work either:

julia> [1]*[1]
no method *(Array{Int64,1},Array{Int64,1})
 in method_missing at /home/jeff/src/julia/jl/base.jl:60

[pao]

Where I see this potentially coming up, it's because some input size may vary and happen to be (1,), so I don't think that [1]*[1] is a good comparison--x*x.' is what you would write (expecting longer vectors), and in my hypothetical it just so happens x==squeeze([1]).

This type just seems like an oddity in the bestiary, but there are many things that are useful that I don't understand.

[JeffBezanson]

I think the real problem here might be that squeeze is just not a very good function. If you want to squeeze something to a vector (for example, a 1x1xNx1x1 thing), you can use reshape instead and be sure to get a vector like you expect.

[pao]

Sounds like a reasonable answer.

[StefanKarpinski]

How about a version of squeeze where you tell it which dimensions you expect to have left in the end — both how many and which ones. Then it can throw an exception if any other dimensions are non-singleton.