CouchDB group view to keep string key and value - couchdb

Question

I have a view with documents in the form of {key:[year,month,day,string],value:int}:
{
rows:[
{
key: [
2016,
4,
30,
"String1"
],
value: 20
},
{
key: [
2016,
4,
30,
"String2"
],
value: 7
},
{
key: [
2016,
4,
30,
"String3"
],
value: 13
},{
key: [
2016,
5,
1,
"String1"
],
value: 10
},
{
key: [
2016,
5,
1,
"String4"
],
value: 12
},{
key: [
2016,
5,
2,
"String1"
],
value: 3
},
]}
From this I use startkey and endkey to get a range of values by date. My issue is then grouping the documents I get returned by the key string, and summing the value int. The rest of the key may or may not be present it does not matter. So far with group levels I have only been able to sum values per date key.
When rendered in a table I get something like:
What I want is:

Answer 1

So I ended up reducing in my controller with javascript like:
$scope.reduceMap = function (rows) {
var reducedMap = {};
var sortableArray = [];
for (var i = 0; i < rows.length; i++) {
var key = rows[i].key[3];
if (!reducedMap.hasOwnProperty(key)) {
reducedMap[key] = {key: key, value: rows[i].value};
} else {
reducedMap[key] = {key: key, value: rows[i].value + reducedMap[key].value};
}
}
for (var k in reducedMap) {
sortableArray.push(reducedMap[k]);
}
return sortableArray;
};
Since I asked for a CouchDB answer, I will leave this here but not accept it.

Answer 2

If you emit view's key as: string, year, month, day and use a built in reduce function _sum, then the following URL example gives you the desired result:
http://localhost:5984/text/_design/search/_view/by_text?startkey=["",2016,1,1]&endkey=[{},2016,1,1]&group_level=1
Your date search criteria is specified as normal, but the first part of the key is basically any string. Then grouping level 1 and reducing using sum gives you the count of string occurrences withing date range grouped by string.