Underscore.js .filter() and .any()

Question

I have an array of event objects called events . Each event has markets , an array containing market objects. Inside here there is another array called outcomes , containing outcome objects.

In this question , I asked for a [Underscore.js] way to find all of the events which have markets which have outcomes which have a property named test . The answer was:

// filter where condition is true
_.filter(events, function(evt) {

    // return true where condition is true for any market
    return _.any(evt.markets, function(mkt) {

        // return true where any outcome has a "test" property defined
        return _.any(mkt.outcomes, function(outc) {
            return outc.test !== "undefined" && outc.test !== "bar";
        });
    });
});

This works great, but I'm wondering how I would alter it if I wanted to filter the outcomes for each market, so that market.outcomes only stored outcomes that were equal to bar . Currently, this is just giving me markets which have outcomes which have some set test properties. I want to strip out the ones that do not.

Answer 1

Make it a simple loop, using the splice method for the array removals:

var events = [{markets:[{outcomes:[{test:x},...]},...]},...];
for (var i=0; i<events.length; i++) {
    var mrks = events[i].markets;
    for (var j=0; j<mrks.length; j++) {
        var otcs = mrks[j].outcomes;
        for (var k=0; k<otcs.length; k++) {
            if (! ("test" in otcs[k]))
                 otcs.splice(k--, 1); // remove the outcome from the array
        }
        if (otcs.length == 0)
            mrks.splice(j--, 1); // remove the market from the array
    }
    if (mrks.length == 0)
        events.splice(i--, 1); // remove the event from the array
}

This code will remove all outcomes that have no test property, all empty markets and all empty events from the events array.

An Underscore version might look like that:

events = _.filter(events, function(evt) {
    evt.markets = _.filter(evt.markets, function(mkt) {
        mkt.outcomes = _.filter(mkt.outcomes, function(otc) {
            return "test" in otc;
        });
        return mkt.outcomes.length > 0;
    });
    return evt.markets.length > 0;
});