Question 294319 in Javascript Question posted in
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Javascript – how to search and loop array of object for particular key using recursion

I have a array of objects

  • Some objects have id and some are not
  • those having id can present with either "split" or "relation" key not both
  • inside split there can be another split or relation
  • now I need to read all relation present by digging deeply

I need output like below:

let _rel = [
    {"relation": "a"},
    {"relation": "b"}
]

// my try which is not working 
const getRelations = (arr, _rel=[]) => {
    for(let {uuid, relations, split} of arr){
        if(uuid) {
            if(relations) [..._rel, relations]
            else if(split) {
                getRelations(split)
            }
        }
    }
    return _rel    
}
getRelations(arr)

Input:

let arr = [
            {"start_offset": 0},
            {
                "uuid": "100",
                "relations": [
                    {
                        "relation": "a",
                    }
                ]            
            },
            {"start_offset": 355},
            {
                "uuid": "200",
                "split": [
                    {
                        "uuid": "300",
                        "split": [
                            {
                                "uuid": "400",
                                "relations": [
                                    {
                                        "relation": "b",
                                    }
                                ]
                            }
                        ]
                    },
                    {
                        "uuid": "500",
                    }
                ],
            },
            {"start_offset": 689}
]

// my try which is not working 
const getRelations = (arr, _rel=[]) => {
    for(let {uuid, relations, split} of arr){
        if(uuid) {
            if(relations) [..._rel, relations]
            else if(split) {
                getRelations(split)
            }
        }
    }
    return _rel    
}
getRelations(arr)
Tags:

4

Answers


  1. 0

    You need to assign the result of the spread operation to _rel when you have relations in order to accumulate the values.
    When you recursively call getRelations(split), you should merge the results with _rel.

    EDIT
    Pure javascript (wrong react)

    You can make sure the function works with arrays of any type by using a generic parameter

    const getRelations = (arr, _rel = []) => {
    for (let { uuid, relations, split } of arr) {
        if (uuid) {
            if (relations) {
                _rel.push(...relations);
            } else if (split) {
                getRelations(split, _rel);
            }
        }
    }
    return _rel;
};

const arr = [
    { "start_offset": 0 },
    {
        "uuid": "100",
        "relations": [
            {
                "relation": "a",
            }
        ]
    },
    { "start_offset": 355 },
    {
        "uuid": "200",
        "split": [
            {
                "uuid": "300",
                "split": [
                    {
                        "uuid": "400",
                        "relations": [
                            {
                                "relation": "b",
                            }
                        ]
                    }
                ]
            },
            {
                "uuid": "500",
            }
        ]
    },
    { "start_offset": 689 }
];

const result = getRelations(arr);
console.log(result);
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  2. 0

    You could take a check and return a flat array of relations or an empty array.

    const
    data = [{ start_offset: 0 }, { uuid: "100", relations: [{ relation: "a" }] }, { start_offset: 355 }, { uuid: "200", split: [{ uuid: "300", split: [{ uuid: "400", relations: [{ relation: "b" }] }] }, { uuid: "500" }] }, { start_offset: 689 }],
    fn = ({ split, relations }) => split
        ? split.flatMap(fn)
        : relations || [],
    getRelations = array => array.flatMap(fn);

console.log(getRelations(data));
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  3. 0

    A couple of changes:

    1- When you have relations, push the { "relation": relations }
    object into the _rel array.

    2- When you have split, recursively call getRelations with the split array and pass the existing _rel array.

    Now, the relations array should be correctly populated with the desired output.

    const getRelations = (arr, _rel = []) => {
  for (let {
      uuid,
      relations,
      split
    } of arr) {
    if (uuid) {
      if (relations) {
        _rel.push({
          "relation": relations
        });
      } else if (split) {
        getRelations(split, _rel);
      }
    }
  }
  return _rel;
};


const arr = [{
    uuid: "1",
    relations: "a",
    split: [{
      uuid: "2",
      relations: "b"
    }]
  },
  {
    uuid: "3",
    split: [{
      uuid: "4",
      relations: "c"
    }]
  },
];

const relations = getRelations(arr);
console.log(relations);
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  4. 0

    An one-liner:

    const data = [{ start_offset: 0 }, { uuid: "100", relations: [{ relation: "a" }] }, { start_offset: 355 }, { uuid: "200", split: [{ uuid: "300", split: [{ uuid: "400", relations: [{ relation: "b" }] }] }, { uuid: "500" }] }, { start_offset: 689 }];

const getRelations = (items, out = []) => (items.forEach(item => item.split ? getRelations(item.split, out) : item.relations && out.push(...item.relations)), out);

console.log(getRelations(data));
    ` Chrome/119
-----------------------------------------------------------
Alexander      1.00x  |  x10000000  567  571  573  589  590
Nina Scholz   11.09x  |   x1000000  629  630  633  648  659
-----------------------------------------------------------
https://github.com/silentmantra/benchmark `

    const data = [{ start_offset: 0 }, { uuid: "100", relations: [{ relation: "a" }] }, { start_offset: 355 }, { uuid: "200", split: [{ uuid: "300", split: [{ uuid: "400", relations: [{ relation: "b" }] }] }, { uuid: "500" }] }, { start_offset: 689 }];

//@benchmark Nina Scholz

const fn = ({ split, relations }) => split
        ? split.flatMap(fn)
        : relations || [],
    getRelations = array => array.flatMap(fn);

getRelations(data);


//@benchmark Alexander 
{
const getRelations = (items, out = []) => (items.forEach(item => item.split ? getRelations(item.split, out) : item.relations && out.push(...item.relations)), out);
getRelations(data);

}


/*@end*/eval(atob('e2xldCBlPWRvY3VtZW50LmJvZHkucXVlcnlTZWxlY3Rvcigic2NyaXB0Iik7aWYoIWUubWF0Y2hlcygiW2JlbmNobWFya10iKSl7bGV0IHQ9ZG9jdW1lbnQuY3JlYXRlRWxlbWVudCgic2NyaXB0Iik7dC5zcmM9Imh0dHBzOi8vY2RuLmpzZGVsaXZyLm5ldC9naC9zaWxlbnRtYW50cmEvYmVuY2htYXJrL2xvYWRlci5qcyIsdC5kZWZlcj0hMCxkb2N1bWVudC5oZWFkLmFwcGVuZENoaWxkKHQpfX0='));
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