Iterable JuMPArray

[ccoffrin]

It would be nice if the JuMPArray was iterable for clean use in for loops.

[mlubin]

What do you want this to look like? JuMPArray is sort of more like a dictionary than an array. You can use keys to iterate through it (see #646).

[ccoffrin]

Aaa I see. With a generic Julia Dict you can do this,

for (k,v) in dict
   println(k) #key
   println(v) #value
end

which can cover the case when you only need the key or the value as well as when you want both. What do you think about adding support for that?

[mlubin]

The larger issue is the inconsistencies between Array{Variable} and JuMPArray{Variable}, because sometimes it's a JuMP artifact which type is returned:

S = 1:3
x = @variable(m, [S]) # JuMPArray
y = @variable(m, [1:3]) # Julia Array

It's a bad idea to have different iteration syntax for x and y, so I'd like to figure out a consistent global approach (including solving #646) before adding any new features that might be broken later.

[ccoffrin]

Agreed, this is a bigger issue. My first impression is that JuMPArray is a more general data-structure so that could be the standard type to return. Then you only need to define iteration over JuMPArrays and its always consistent.

As a side note, in my case I am using getvariable(m, symbol) and getting a JuMPArray.

[mlubin]

If you're indexing over anything other than a product of 1-based ranges, then you won't get a plain Julia array.