Question

Is there a way in JavaScript to select a element of a multidimential array. Where the depth/rank/dimensionality is variable and the keys are given by a array of indices. Such that i don’t have handle every possible dimentional depth separately. concretely speaking i want do get rid of switch cases like here:

/**
 * set tensor value by index
 * @type {array} indices [ index1, index2, index3 ] -> length == rank.
 * @type {string} value.
 */
tensor.prototype.setValueByIndex = function( indices, value ) {
    var rank = indices.length;

    switch(rank) {
        case 0:
            this.values[0] = value;
        break;
        case 1:
            this.values[indices[0]] = value;
        break;
        case 2:
            this.values[indices[0]][indices[1]] = value;
        break;
        case 3:
            this.values[indices[0]][indices[1]][indices[2]] = value;
        break;
    }
}

Where this.values is a multidimensional array.

such that i get something that looks more like this:

/**
 * set tensor value by index
 * @type {array} indices, [ index1, index2, index3 ] -> length == rank
 * @type {string} value
 */
tensor.prototype.setValueByIndex = function( indices, value ) {
    var rank = indices.length;

    this.values[ indices ] = value;
}

Thank you in advance!

Answer 1

tensor.prototype.setValueByIndex = function( indices, value ) {
    var array = this.values;
    for (var i = 0; i < indices.length - 1; ++i) {
        array = array[indices[i]];
    }
    array[indices[i]] = value;
}

This uses array to point to the nested array we are currently at and reads through the indicies for find the next array value from the current array. Once we reach the last index in the indices list, we have found the array where we want to deposit the value. The final index is the slot in that final array where we deposit the value.