how to get total value of array object values using dynamic keys

Question

I have the following mock array,

this array is demo purpose, owlCount doesnt make sense i know.

let arr = [
    {
        "id": "000701",
        "status": "No Source Info",
        "sources": []
    },
    {
        "id": "200101",
        "status": "Good",
        "sources": [
            {
                "center": "H2",
                "uri": "237.0.1.133",
                "owlCount": 1,
                "status": "Good",
                "state": {
                    "authState": "authorized",
                    "lockState": "locked"
                }
            }
        ]
    },
    {
        "id": "005306",
        "status": "Good",
        "sources": [
            {
                "center": "H1",
                "uri": "237.0.6.5",
                "owlCount": 3,
                "status": "Good",
                "state": {
                    "authState": "authorized",
                    "lockState": "locked"
                }
            },
            {
                "center": "H1",
                "uri": "237.0.6.25",
                "owlCount": 5,
                "status": "Good",
                "state": {
                    "authState": "authorized",
                    "lockState": "locked"
                }
            }
        ]
    }
]

How would i go about using reduce to add the values owlCount within each nested array. Without doing [0] to get within the nested array

I was thinking of something like this, but i get the value of 0, when it should be 9

const sum = arr.reduce( (acc, cv, i) => {
    acc[i] += cv.owlCount
return acc
}, 0)

What am i doing wrong, and what should be the solution.

Dhananjai Pai · Accepted Answer · 2019-10-08 22:52:06Z

here acc is a number not an array, not sure why you would use acc[i] ? You will have to run two reduce loops here. One for outer array and one for inner array to get the sum of owlCount from sources.

let arr = [
    {
        "id": "000701",
        "status": "No Source Info",
        "sources": []
    },
    {
        "id": "200101",
        "status": "Good",
        "sources": [
            {
                "center": "H2",
                "uri": "237.0.1.133",
                "owlCount": 1,
                "status": "Good",
                "state": {
                    "authState": "authorized",
                    "lockState": "locked"
                }
            }
        ]
    },
    {
        "id": "005306",
        "status": "Good",
        "sources": [
            {
                "center": "H1",
                "uri": "237.0.6.5",
                "owlCount": 3,
                "status": "Good",
                "state": {
                    "authState": "authorized",
                    "lockState": "locked"
                }
            },
            {
                "center": "H1",
                "uri": "237.0.6.25",
                "owlCount": 5,
                "status": "Good",
                "state": {
                    "authState": "authorized",
                    "lockState": "locked"
                }
            }
        ]
    }
]
const sum = arr.reduce( (acc, item) => {
    return acc += item.sources.reduce((a,source) => a += source.owlCount ,0)
}, 0)

console.log(sum);

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