JavaScript Array.sample and Object.traverse

traverse.js

function sample(opts, num){
    // like python sample
    var choice,
        choices = [];
    while(choices.length < num && choices < opts.length){
        choice = parseInt(Math.random() * opts.length);
        if(choices.indexOf(choice) == -1){
            choices.push(choice);
        }
    }
    return choices.map(function(c){return opts[c]});
}

function traverse(item, axis, found){
    /*
        returns all items on the provided axis (named property)
        
        memoization is attractive, but the immediate case wouldn't be
        able to make use of it
    */
    found = arguments.length == 2 ? [item] : found;
    
    return item[axis]
        .filter(function(item){
            return !found || found.indexOf(item) == -1;
        })
        .reduce(function(found, item){
            found.push(item);
            return traverse(item, axis, found);
        }, found)
}

// simple test data
var data = [];

for (var i=0; i<100; i++){
    data.push({
        id: i,
        axis1: sample(data, parseInt(Math.random() * 3)),
        axis2: sample(data, parseInt(Math.random() * 2)),
    });
}