Add trivial case to _reshape function

[zhao-18]

I recently had a case where the new dimensions of a matrix were [1, 1, 1, 1, 318, 512, 512]. I attempted to use the reshape function, but it was hitting the heap limit and failing. I ended up importing the function and adding a case where if the size of a dimension is 1, don't do anything and keep going. That seemed to work well.
I do not think having 1 size for a dimension is common, but in some cases I definitely think it is a improvement. The following is the modification I made.

function _reshape (array, sizes) {
  // testing if there are enough elements for the requested shape
  let tmpArray = array
  let tmpArray2
  // for each dimensions starting by the last one and ignoring the first one
  for (let sizeIndex = sizes.length - 1; sizeIndex > 0; sizeIndex--) {
    const size = sizes[sizeIndex]
    if ( size == 1 ) continue // <=== Added trivial case check
    tmpArray2 = []

    // aggregate the elements of the current tmpArray in elements of the requested size
    const length = tmpArray.length / size
    for (let i = 0; i < length; i++) {
      tmpArray2.push(tmpArray.slice(i * size, (i + 1) * size))
    }
    // set it as the new tmpArray for the next loop turn or for return
    tmpArray = tmpArray2
  }

  return tmpArray
}

[gwhitney]

I recently had a case where the new dimensions of a matrix were [1, 1, 1, 1, 318, 512, 512]. I attempted to use the reshape function, but it was hitting the heap limit and failing.

If a mathjs function crashes on a valid input, that is a bug. Please file this example as an issue, thank you.

On the other hand, as to your suggested code, it cannot be correct to continue for a dimension of size 1; that would amount to ignoring the dimension. For a correct return value, each dimension must correspond to a layer of array bracketing. E.g, in the demo REPL on https://mathjs.org:

reshape([1,2,3;4,5,6],[6])
  [1, 2, 3, 4, 5, 6]
reshape([1,2,3;4,5,6],[6,1])
  [[1], [2], [3], [4], [5], [6]]
reshape([1,2,3;4,5,6],[6,1,1])
  [[[1]], [[2]], [[3]], [[4]], [[5]], [[6]]]

If I am reading your code correctly, it would return the same thing on all three of these inputs?

Of course, some matrices may simply be too large to represent in memory. However, your example does not crash on my machine:

const mat = math.range(0, 318*512*512)
console.log(mat.size())
const mat2 = math.reshape(mat, [1, 1, 1, 1, 318, 512, 512])
console.log(mat2.size())

successfully prints out

[ 83361792 ]
[
    1,   1,   1, 1,
  318, 512, 512
]

and runs to completion. So please if/when you do file an issue, please post as exact a way as possible to generate the crash, and make sure to note what environment you are running mathjs in (I ran the above code in Node v22.13.1, for example; but perhaps it does crash some browser when it runs in-browser -- just let us know the details of how you are running it).
If you do file an issue, then please close this discussion. Thanks.

[zhao-18]

You are absolutely correct on the brackets.

The code was part of larger program where I was porting MatLab script into JavaScript, and there are lot of inefficiencies in memory management that I am aware.

Thank you for your thorough reply. I will close this discussion.