I have the following collection with c array inside each document
{
{
id: 1,
k: 2.2,
type: "dog",
c: [ {parentId:1, p:2.2}, {parentId:1, p:1.4} ]
},
{
id: 2,
k: 4.3,
type:"cat",
c: [ {parentId:2, p:5.2}, {parentId:2, p:4.5} ]
}
}
parentId inside each subdocument in c is id of containing document.
I want to group all docs by type and in each group know sum of k and sum of all p in all arrays of the group.
Currently I do summation of k in the group stage but summation of p in the result array in the application. I want to do summation of p in DB!
This is what I do currently:
db.myCol.aggregate([
{
$group: {
_id: { type: '$type'},
k: {$sum: '$k'}, // sum k values, very easy!
// p: {$sum: '$c.0.p'} <==== Does not work, too
c: {$addToSet: '$c'} // add to each group all c arrays of group's members
}
}
], function(err, res) {
// go over c-arrays and sum p values
var accP = 0; // accumulator for p values
for ( var i=0; i<res.length; i++ ) {
var c = res[i].c;
for (var j=0;j<c.length; j++) {
var c2 = c[j];
for ( var k=0; k<c2.length; k++) { // finally got to objects c array
accP += c2[k].p;
}
}
res[i].c = accP; // replace array with accumulated p value
}
});
