reshape()

[patgrasso]

I think it might be useful to have a reshape() function that accepts a matrix and a list of dimensions, and formats the matrix to fit the specified dimensions. resize() does this already, but it doesn't preserve all of the elements.

var A = [1, 2, 3, 4, 5, 6, 7, 8, 9];
A.resize([3, 3]);
/* => [[1, 0, 0],
       [2, 0, 0],
       [3, 0, 0]] */
A.reshape([3, 3]);
/* => [[1, 2, 3],
       [4, 5, 6],
       [7, 8, 9]] */

Thoughts? I can start working on it and submit a PR if this sounds appealing.

[josdejong]

A function reshape is a common utility and would be complementary to resize. I personally haven't seen any use cases for it though: normally the rows and columns of a matrix containing data have a meaning. Like storing 3d points in rows, where columns 0, 1, 2 hold the x, y, and z location of the points. "Reshuffling" the data points using a function reshape simply turns the data in a bunch of meaningless numbers.

Do you have any practical use cases for reshape?

[patgrasso]

Primarily as a facilitation when generating data to work with.
For instance, reshaping a range or random data:

var A = math.range(1, 10).reshape([3, 3]);
var B = math.random(0, 1).reshape([2, 3]);
// this is equal to math.random([2, 3]);

Or perhaps even adding this functionality to range(), as it exists for random(), however if for some reason you wanted to use the function outside of these two instances, you wouldn't be able to without the standalone reshape() function.

[ericman314]

In the past I have used matlab's reshape function to reconstruct a multi-dimensional array that had been serialized to a file. For example,

// f is some interesting function we wish to study

for(var i=0; i<10; i++) {
  for(var j=0; j<10; j++) {
    for(var k=0; k<10; k++) {
      fs.appendLine("myfile.txt", f(i, j, k));
    }
  }
}

Later,

// loadMyArray is some function to read a file into an array

var flat = loadMyArray("myfile.txt");
var array = flat.reshape(10, 10, 10);
// Array is now a multidimensional array

Came in very handy to reshape data so it could be plotted by matlab.

[josdejong]

Thanks for the examples guys. reshape can indeed be a handy construction utility.

@patgrasso it would be great if you want to implement reshape, thanks for the offer!

[iahu]

reshape is useful. for example, to transform a 1d image pixel data array to a M*N shape matrix.

const pixelData = [255, 255, 255, 255, ....]; // a 1d Buffer array
reshape(pixelData, 20, 20);