distinct value with count and condition mongo DB - regex

Question

I am new to MongoDB, and so far it seems like it is trying to go out of it's way to make doing simple things overly complex.
I am trying to run the below MYSQL equivalent
SELECT userid, COUNT(*)
FROM userinfo
WHERE userdata like '%PC% or userdata like '%wire%'
GROUP BY userid
I have mongo version 3.0.4 and i am running MongoChef.
I tried using something like the below:
db.userinfo.group({
"key": {
"userid": true
},
"initial": {
"countstar": 0
},
"reduce": function(obj, prev) {
prev.countstar++;
},
"cond": {
"$or": [{
"userdata": /PC/
}, {
"userdata": /wire/
}]
}
});
but that did not like the OR.
when I took out the OR, thinking I’d do half at a time and combine results in excel, i got an error "group() can't handle more than 20000 unique keys", and the result table should be much bigger than that.
From what I can tell online, I could do this using aggregation pipelines, but I cannot find any clear examples of how to do that.
This seems like it should be a simple thing that should be built in to any DB, and it makes no sense to me that it is not.
Any help is much appreciated.

Answer 1

/
Works "sooo" much better with the .aggregate() method, as .group() is a very outmoded way of approaching this:
db.userinfo.aggregate([
{ "$match": {
"userdata": { "$in":[/PC/,/wire/] }
}},
{ "$group": {
"_id": "$userid",
"count": { "$sum": 1 }
}}
])
The $in here is a much shorter way of writing your $or condition as well.
This is native code as opposed to JavaScript translation as well, so it runs much faster.

Answer 2

Here is an example which counts the distinct number of first_name values for records with a last_name value of “smith”:
db.collection.distinct("first_name", {“last_name”:”smith”}).length;
output
3