How to divide the elements inside array using mongodb aggregation - mongodb

Question

I have used aggregation to find below output.
Next step is to divide the values of elements present in each array.
{
"_id" : {
“type”:”xxx”,
"year" : 2019
},
"allvalues" : [
{
"label" : “used”,
"value" : 50
},
{
"label" : “total”,
"value" : 58
}
]
}
{
"_id" : {
“type”:”yyy”,
"year" : 2019
},
"allvalues" : [
{
"label" : “used”,
"value" : 63.214285714285715
},
{
"label" : “total”,
"value" : 59.535714285714285
}
]
}
How to write the query to divide used/total in each doc.
For first doc it is 50/58 and second doc it is 63.21/59.53.
The structure of json remains constant.
Output should look like below:
{
“type”:”xxx”,
"year" : 2019,
“result” : 0.8
}
{
“type”:”yyy”,
"year" : 2019,
“result” : 1.06
}

Answer 1

Add this in the aggregate pipeline after you get above input first you need to use $filter and $arrayElemAt to get used and total's value after that as divide doesn't give fixed decimal place, I've used $trunc to make value to 2 decimal fixed place
{
$project: {
_id: 1,
used: {
$arrayElemAt: [
{
$filter: {
input: "$allvalues",
as: "item",
cond: {
$eq: [
"$$item.label",
"used"
]
}
}
},
0
]
},
total: {
$arrayElemAt: [
{
$filter: {
input: "$allvalues",
as: "item",
cond: {
$eq: [
"$$item.label",
"total"
]
}
}
},
0
]
},
}
},
{
$project: {
_id: 1,
result: {
$divide: [
{
$trunc: {
$multiply: [
{
$divide: [
"$used.value",
"$total.value"
]
},
100
]
}
},
100
]
}
}
}