Mongodb filter results with unique value - node.js

Question

I have a collections of bunch of cities and zip codes, where name of a city can be a same, while zip code is different.
I'm trying to query thru all cities starting with 'San' for example and want to filter results where San Antonio appears only ones along with any other cities starting with San.
Here is a code I use:
Zipcodes.find(
{ city: { $regex: /San/, $options: 'i' } },
(err, result) => {
if (err) {
return res.send({ error: err });
}
res.send({ data: result });
},
).limit(20);
This given me following results:
{
"loc": [
-94.132581,
31.515173
],
"_id": "75972",
"city": "SAN AUGUSTINE",
"pop": 5916,
"state": "TX"
},
{
"loc": [
-98.730929,
31.162678
],
"_id": "76877",
"city": "SAN SABA",
"pop": 4023,
"state": "TX"
},
{
"loc": [
-100.481752,
31.478165
],
"_id": "76901",
"city": "SAN ANGELO",
"pop": 23800,
"state": "TX"
},
{
"loc": [
-100.480036,
31.419411
],
"_id": "76904",
"city": "SAN ANGELO",
"pop": 25535,
"state": "TX"
},
{
"loc": [
-100.390005,
31.464738
],
"_id": "76905",
"city": "SAN ANGELO",
"pop": 11284,
"state": "TX"
},
{
"loc": [
-100.438586,
31.470735
],
"_id": "76903",
"city": "SAN ANGELO",
"pop": 32471,
"state": "TX"
},
{
"loc": [
-95.034496,
29.466033
],
"_id": "77539",
"city": "SAN LEON",
"pop": 21905,
"state": "TX"
},
{
"loc": [
-99.427148,
27.062523
],
"_id": "78067",
"city": "SAN YGNACIO",
"pop": 871,
"state": "TX"
},
{
"loc": [
-98.460127,
29.414799
],
"_id": "78203",
"city": "SAN ANTONIO",
"pop": 7261,
"state": "TX"
},
{
"loc": [
-98.525967,
29.422855
],
"_id": "78207",
"city": "SAN ANTONIO",
"pop": 58355,
"state": "TX"
},
{
"loc": [
-98.5063,
29.400217
],
"_id": "78204",
"city": "SAN ANTONIO",
"pop": 11526,
"state": "TX"
},
{
"loc": [
-98.479338,
29.441338
],
"_id": "78215",
"city": "SAN ANTONIO",
"pop": 1264,
"state": "TX"
},
{
"loc": [
-98.545219,
29.358366
],
"_id": "78211",
"city": "SAN ANTONIO",
"pop": 30417,
"state": "TX"
},
{
"loc": [
-98.492509,
29.423711
],
"_id": "78205",
"city": "SAN ANTONIO",
"pop": 1714,
"state": "TX"
},
{
"loc": [
-98.497511,
29.533387
],
"_id": "78216",
"city": "SAN ANTONIO",
"pop": 30435,
"state": "TX"
},
{
"loc": [
-98.419444,
29.539525
],
"_id": "78217",
"city": "SAN ANTONIO",
"pop": 27925,
"state": "TX"
}
It's returning San Antonio many times. I need only ones.
Please help with a correct query. Thanks.

Answer 1

You can use $group + $replaceRoot to get values unique by city:
db.collection.aggregate([
{
$match: { city: { $regex: "San", $options: "i" } }
},
{
$group: {
_id: "$city",
doc: { $first: "$$ROOT" }
}
},
{
$replaceRoot: {
newRoot: "$doc"
}
}
])
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