t = db.mr_merge;
t.drop();

t.insert({a: [1, 2]});
t.insert({a: [2, 3]});
t.insert({a: [3, 4]});

outName = "mr_merge_out";
out = db[outName];
out.drop();

m = function() {
    for (i = 0; i < this.a.length; i++)
        emit(this.a[i], 1);
};
r = function(k, vs) {
    return Array.sum(vs);
};

function tos(o) {
    var s = "";
    for (var i = 0; i < 100; i++) {
        if (o[i])
            s += i + "_" + o[i];
    }
    return s;
}

res = t.mapReduce(m, r, {out: outName});

expected = {
    "1": 1,
    "2": 2,
    "3": 2,
    "4": 1
};
assert.eq(tos(expected), tos(res.convertToSingleObject()), "A");

t.insert({a: [4, 5]});
out.insert({_id: 10, value: "5"});
res = t.mapReduce(m, r, {out: outName});

expected["4"]++;
expected["5"] = 1;
assert.eq(tos(expected), tos(res.convertToSingleObject()), "B");

t.insert({a: [5, 6]});
out.insert({_id: 10, value: "5"});
res = t.mapReduce(m, r, {out: {merge: outName}});

expected["5"]++;
expected["10"] = 5;
expected["6"] = 1;

assert.eq(tos(expected), tos(res.convertToSingleObject()), "C");

// test that the nonAtomic output gives valid result
t.insert({a: [6, 7]});
out.insert({_id: 20, value: "10"});
res = t.mapReduce(m, r, {out: {merge: outName, nonAtomic: true}});

expected["6"]++;
expected["20"] = 10;
expected["7"] = 1;

assert.eq(tos(expected), tos(res.convertToSingleObject()), "D");