path: root/js/reshape.js

// more details, <https://eli.li/reshape-in-javascript-and-apl>

function ravel(array) {
  if (!Array.isArray(array)) return [array];
  return array.flatMap(val => ravel(val));
}

function reshape(shape, array) {
  const totalSize = shape.reduce((acc, val) => acc * val, 1);
  const ravelledArray = ravel(array);
  const filledArray = Array.from({ length: totalSize }, (_, i) => ravelledArray[i % ravelledArray.length]);

  // This function builds a nested array based on the given shape and data.
  // It recursively constructs the nested array by slicing the data array and creating subarrays.
  // The offset parameter is used to keep track of the current position in the data array.
  function buildNestedArray(shape, data, offset = 0) {
    // If the shape has only one element, return a slice of the data array with the specified size.
    if (shape.length === 1) {
      return data.slice(offset, offset + shape[0]);
    }

    // Extract the first element of the shape array as the size of the current dimension.
    // The remaining elements form the subshape.
    const [size, ...subShape] = shape;

    // Calculate the size of the subarray for the next dimension.
    const subArraySize = subShape.reduce((acc, val) => acc * val, 1);

    // Create an array of size 'size' and recursively call buildNestedArray for each element.
    return Array.from({ length: size }, (_, i) => buildNestedArray(subShape, data, offset + i * subArraySize));
  }

  return buildNestedArray(shape, filledArray);
}