Efficient Cell Array data structure walker. (No functions. No recursion.)

streaming-cross-join-walker.js

// The following is useful when building a
// streaming cartesian product (ie. cross join)
// e.g., Imagine walking a two-dimensional matrix
//   having one [column] dimension given and fixed at initialization,
//   and one dimension of varying, perhaps infinite, lengths [determined by each row].
//   A set of nested for...loop would normally accomplish this,
//   if it weren't for the number of loop statements required varying by invocation.

const size = 3; // matrix size variable
const len = [3,2,3]; // the length of each list in the matrix (notice they can vary)
const cur = [0,0,0]; // the current position / cursor in each list
let p = 0; // a stack pointer used when incrementing the cursor position through each list

// visit every position in the matrix, the same way a set of nested for...loops would
while (p === 0) {
    // do stuff
    console.log(`pos=${cur.join(',')}`);

    // step
    cur[0]++;
    while (cur[p] === len[p]) {
        cur[p] = 0;
        ++p;
        // if we have incremented the root-most loop beyond its length
        if (p >= size) {
            // could also return; we're done
            break;
        }
        cur[p] += 1;
        if (cur[p] !== len[p]) {
            p = 0;
            break;
        }
    }
}

console.log('done');