Initializing JavaScript array based on user input

Question

I have an applet that allows the user to define values for 10 variables, all of which could be arrays. I then want the program to iterate over all possible combinations and then save the calculations to a variable.

Previously I hard-coded it to initialize the result array, SIGMA, by looping over every variable, regardless of if it is a vector or a single value, IE:

SIGMA = new Array(A.length);
for (i1=0; i1<A.length; i1++) {
  SIGMA[i1] = new Array(B.length);
  for (i2=0; i2<B.length; i2++) {
    SIGMA[i1][i2] = new Array(C.length);
    for (i3=0; i3<C.length; i3++) {
      ...
    }
  }
}

This results in a 10-dimensional SIGMA array, which makes processing really slow if a few or more variables are arrays.

What I'd like to do is to have it initialize SIGMA only for those variables that are an array and not a singular value. Therefore, if all variables are a single number except for two, say X and Y, then I'd want to have:

SIGMA = new Array(X.length);
for (i1=0; i1<X.length; i1++) {
  SIGMA[i1] = new Array(Y.length);
}

However, I'm not quite sure how the best way to do this would be, as the number of for loops would depend on the number of variables that are arrays. I'm thinking I either need to use a recursive function or somehow incorporate a while loop.

Anybody have any good ideas on how this can be done? Thanks!

score 0 · Accepted Answer · answered Nov 02 '11 at 22:47

I was able to solve this problem by making a recursive function that included the for loops:

sigma = new Array(eval(var_idx[0]).length);
sigma_forloop('sigma', 0)

function sigma_forloop(X, idx) {
    for (var i=0; i<eval(var_idx[idx]).length; i++) {
        eval(X + '[' + i + ']' + ' = new Array(eval(var_idx[idx+1]).length);')
        if (idx+2 < var_idx.length) {
            var Y = X + '[' + i + ']';
            sigma_forloop(Y, idx+1);
        }
    }
}

The variable 'var_idx' in an array of strings containing the variables that have more than one value, therefore, it's those variables that I want to loop over.

I'm sure there's an easier way of doing it, but this works for now.

That it is...that it is. My experience with JavaScript is very limited, so I'm just happy when something actually works. Is there a much easier way to accomplish this? — Josiah, Nov 02 '11 at 22:59

Initializing JavaScript array based on user input

1 Answers1