Not exactly an issue, but curious about concatenating MultiArrays?

[hollance]

Not exactly an issue, but curious about concatenating MultiArrays?

[hollance]

Can you add a Concat layer to the model? If not, it’s a matter of allocating a large enough memory buffer and copying things by hand. The MultiArray class is really an experimental thing, I wouldn’t use it for serious work.

[jbmaxwell]

Yikes! Is it relatively recently that you've started referring to MultiArray as "experimental"? I've been using it for a while without issue (as long as I avoid [MultiArray] structures—really not sure why that causes problems(??)), so I suppose I'm not too concerned, but it is integrated in my code fairly deeply now. Would you recommend that I remove/replace it?

As far as the concat goes, I could look into the possibility of a concat in my model. For now I've done it by hand, and it seems fine.

[hollance]

Using MultiArray is mostly fine, but there is a known issue with creating a MultiArray derived from another one. In that case it gives the wrong answers. There is a failing test case in the repo in case you're wondering exactly what I'm talking about.

[jbmaxwell]

Ah, okay. Great. Yes, as long as I avoid that I haven't had any trouble. They're handy and helpful (as "helpers", I guess they should be!)

[jbmaxwell]

Quick question: Is there a simple way to get a 3D slice from a 4D MultiArray? I have a MultiArray [4, 3, 64, 64]—i.e., just 4 x [3, 64, 64] images concatenated together—and I want to get the nth [3, 64, 64] sub matrix out.

[hollance]

Grab the pointer to the start of the MLMultiArray and increment it by n*3*64*64 and then copy the next 36464 elements. It’s just a memcpy, basically.

If you want to use MultiArray (without the ML) then you shouldn’t use the pointer but use a for loop and the subscript (because otherwise any reshaping or transposing is ignored). So now you need to loop through the array to copy out the items, which is slower than a single memcpy.

[jbmaxwell]

Thanks, I did wind up iterating over the multiArray.array, but I'll check out the memcpy version. (It's been a long time since I've used memcpy!)