Multidimensional array support

[msakuta]

Now we can declare and define multidimensional arrays

var a: [i32; 2, 3] = [1, 2, 3; 4, 5, 6];

the shape is checked by static type checker, so the following code will be an error, because the assigning value has incompatible shape.

var b: [i32; 3, 2] = [1, 2; 3, 4; 5, 6];
b = [1, 2, 3; 4, 5, 6];

The internal storage for the array is a flattened vec, so that it can be reshaped without modifying the payload.

Added standard functions

Multi-dimensional arrays are hard to write and manipulate in plain code, so we add few standard functions to handle them.

shape

The basic query function to get actual size of an array.

var v: [i64; 2, 3] = [1,2,3;4,5,6];
print(shape(v)); // [2, 3]

transpose

Transposes a 2-D array.

var a: [i32; 2, 3] = [1, 2, 3; 4, 5, 6];

print(a); // [1, 2, 3; 4, 5, 6]

var b: [i32; 3, 2] = transpose(a);

print(b); // [1, 4; 2, 5; 3, 6]

reshape

The most generic way to change shape of 2D matrices. It changes arrangement of dimensions without modifying payload.

var a: [i32; 2, 3] = [1, 2, 3; 4, 5, 6];

print(a); // [1, 2, 3; 4, 5, 6]

var b: [i32; 3, 2] = reshape(a, [3, 2]);

print(b); // [1, 2; 3, 4; 5, 6]

Trying to reshape an array with a different number of elements is an error, even if the target shape is smaller. In other words, it will not be a slice or a view into smaller part of the original array.

reshape([1, 2, 3; 4, 5, 6], [2, 2]);
// Error in run(): Runtime error: reshape's array ([2, 3]) and new shape ([2, 2]) does not have the same number of elements

This behavior may change since we do not want to copy the whole array if the payload doesn't change.

Unfortunately, we cannot check it on compile time, even if we have fixed shape. We may be able to typecheck once we implement generics.

vstack

A frequenty used method to concatenate 2D arrays by stacking vertically in numpy or Matlab.

var a: [i32; 2, 3] = [1, 2, 3; 4, 5, 6];
var b: [i32; 1, 3] = reshape([7, 8, 9], [1, -1]);
var c: [i32; 3, 3] = vstack(a, b);

print(c, shape(c)); // [1, 2, 3; 4, 5, 6; 7, 8, 9] [3, 3]