Count the different variables in an array in my document - rethinkdb

Question

I'm trying out rethinkDB and playing around with some query to see if it could fit by use case. So far, so good. However, I have a question regarding reQL.
For example in this case I store analytics events in rethinkDB such as:
[{
"userId": "abdf213",
"timestamp": "Sat Jan 17 2015 00:32:20 GMT+00:00",
"action": "Page"
},
{
"userId": "123abc",
"timestamp": "Sat Jan 17 2015 00:42:20 GMT+00:00",
"action": "Track"
},
{
"userId": "abdf213",
"timestamp": "Sat Jan 17 2015 00:45:20 GMT+00:00",
"action": "Track"
},
{
"userId": "123abc",
"timestamp": "Sat Jan 17 2015 00:44:20 GMT+00:00",
"action": "Page"
},
{
"userId": "123abc",
"timestamp": "Sat Jan 17 2015 00:48:20 GMT+00:00",
"action": "Page"
}]
I'd like the end result of my query to look like this:
{
"group": "123abc",
"reduction": {
"Page": 2,
"Track": 1
}
},
{
"group": "abdf213",
"reduction": {
"Page": 1,
"Track": 1
}
}
Bear in mind that the action name are not known in advance.
TBH, I'm not quite sure how to achieve this with ReQL.
Right now I have this query (using the data explorer):
r.db('test').table('events').group('userId').map(function(event) {
return event('action')
})
which return doc like this one:
{
"group": "-71omc5zdgdimpuveheqs6dvt5q6xlwenjg7m" ,
"reduction": [
"Identify" ,
"Page" ,
"Track"
]
}
Anyone can point me in the right direction here?
Cheers,
S

Answer 1

Try:
r.table('events').group('userId').map(function(event) {
return r.object(event('action'), 1);
}).reduce(function(a, b) {
return a.merge(b.keys().map(function(key) {
return [key, a(key).default(0).add(b(key))];}).coerceTo('object'));
})

Answer 2

Here's my solution:
r.table("events").group("userId", "action").count().ungroup()
.group(r.row("group")(0))
.map([r.row("group")(1), r.row("reduction")])
.coerceTo("object")
ReQL doesn't support nesting groups, but you can group by multiple fields at the same time and then performing further grouping on the output.