How to reduce nested JSON data structure into a map JavaScript

Question

I've implemented a solution for the problem below with loops, but I'm sure there is a better way. Consider this data structure:

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

I want to learn the most efficient way to reduce it to a map with key-value pairs of only the nested uri and state values from the sources array. The final result should look like this:

let stateMap = {
    "237.0.1.133": { "authState": "authorized", "lockState": "locked" },
    "237.0.6.5": { "authState": "authorized", "lockState": "locked" },
    "237.0.6.25": { "authState": "authorized", "lockState": "locked" } 
}

I have a partial solution that returns a map of each source array, but I'm struggling to get it all into one structure.

let allStates = arr.reduce((acc, object) => {
    if (object.sources.length) {
        let sourceMap = object.sources.reduce((map, obj) => {
            map[obj.uri] = obj.state
            return map
        }, {})
        acc[acc.length] = sourceMap
        return acc
    }
    // delete all unused keys and somehow flatten the objects?
}, {})

Would recursion be an option here or what would be a better approach?

Robby Cornelissen · Accepted Answer · 2018-08-17 05:16:48Z

The code below first performs a flatMap operation on the nested sources arrays, and then reduces everything to your desired result object:

const result = arr.reduce((a, {sources}) => [...a, ...sources], [])
                  .reduce((a, {uri, state}) => ({...a, [uri]: state}), {});

Complete snippet:

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

const result = arr.reduce((a, {sources}) => [...a, ...sources], [])
                  .reduce((a, {uri, state}) => ({...a, [uri]: state}), {});

console.log(result)

Nina Scholz · Accepted Answer · 2018-08-17 06:37:01Z

You could reduce the outer array and iterate sources and update an object as result set.

var data = [{ id: "000701", status: "No Source Info", sources: [] }, { id: "200101", status: "Good", sources: [{ center: "H2", uri: "237.0.1.133", program: 1, status: "Good", state: { authState: "authorized", lockState: "locked" } }] }, { id: "005306", status: "Good", sources: [{ center: "H1", uri: "237.0.6.5", program: 3, status: "Good", state: { authState: "authorized", lockState: "locked" } }, { center: "H1", uri: "237.0.6.25", program: 3, status: "Good", state: { authState: "authorized", lockState: "locked" } }] }],
    stateMap = data.reduce(
        (o, { sources }) => (sources.forEach(({ uri, state }) => o[uri] = state), o),
        Object.create(null)
    );

console.log(stateMap);

.as-console-wrapper { max-height: 100% !important; top: 0; }

Would recursion be an option here or what would be a better approach?

No, because you have only one single nested level.

Prasanna · Accepted Answer · 2018-08-17 05:07:46Z

you can use nested reduce one for getting the uri map from the item in the list, other for getting the value of sources map.

const mappedArray = arr.reduce((acc, item) => ({
  ...acc,
  ...item.sources.reduce((accSource, itemSource) => ({
    ...accSource,
    [itemSource.uri]: itemSource.state,
  }), {})
}), {})

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


const mappedArray = arr.reduce((acc, item) => ({
  ...acc,
  ...item.sources.reduce((accSource, itemSource) => ({
    ...accSource,
    [itemSource.uri]: itemSource.state,
  }), {})
}), {})

console.log(mappedArray)

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