t = db.mr_index2;
t.drop();

t.save({arr: [1, 2]});

map = function() {
    emit(this._id, 1);
};
reduce = function(k, vals) {
    return Array.sum(vals);
};

res = t.mapReduce(map, reduce, {out: "mr_index2_out", query: {}});
assert.eq(1, res.counts.input, "A");
res.drop();

res = t.mapReduce(map, reduce, {out: "mr_index2_out", query: {arr: {$gte: 0}}});
assert.eq(1, res.counts.input, "B");
res.drop();

t.ensureIndex({arr: 1});
res = t.mapReduce(map, reduce, {out: "mr_index2_out", query: {arr: {$gte: 0}}});
assert.eq(1, res.counts.input, "C");
res.drop();