mapreduce_example

function city_map() {
    emit({state:this.state, city:this.city}, {zips:1, pop:this.pop});
}

function city_reduce(key, values) {
    out = {zips:0, pop:0};
    values.forEach(function (val) {
        out.zips += val.zips;
        out.pop += val.pop;
    });
    return out;
}

function city_finalize(key, val) {
    val.people_per_zip = val.pop / val.zips;
    return val;
}


function state_map() {
    emit(this._id.state, {zips:this.value.zips, pop:this.value.pop, cities:1});
}

function state_reduce(key, values) {
    out = {zips:0, pop:0, cities:0};
    values.forEach(function (val) {
        out.zips += val.zips;
        out.pop += val.pop;
        out.cities += val.cities;
    });
    return out;
}

function state_finalize(key, val) {
    val.people_per_zip  = val.pop / val.zips;
    val.people_per_city = val.pop / val.cities;
    val.zips_per_city   = val.zips / val.cities;
    return val;
}