Question

Technologies:

javascript

Tolerim

a month ago

How can I combine the objects in a linear array with those in a nested array?

Currently, there are two arrays A and B that contain objects. A is an existing array, and B is the array used to mutate A. To merge B into A, the following requirements should be met:

If a member of B exists in A, the A object needs to be replaced in place with the B object. However, all properties from the A object should be retained, overwriting any matching properties with the properties of the B object.
If a member of B does not exist in A, it needs to be added to the array as a sibling of the first object in A.

It's crucial to note that the above approach only works for linear objects and breaks down when objects have children. A better approach is required to work with complex objects. Below are the two arrays that need to be merged, A and B:

let a = [
  {
    "key": "parent-1",
    "type": "parent",
    "items": [
      {
        "key": "parent-1-1",
        "type": "parent",
        "items": [
          {
              "key": "child-1-1",
              "dataType": "text",
              "description": "foo",
              "someproperty": "stays"
          }
        ]
      },
      {
        "key": "parent-1-2",
        "type": "parent",
        "items": [
          {
            "key": "child-1-2",
            "dataType": "text"
          }
        ]
      }
    ]   
  }
]

let b = [
  {
      "key": "child-1-1",
      "dataType": "text",
      "description": "bar"
  },
  {
      "key": "child-2",
      "dataType": "text",
      "description": "As this does not appear in A, it will be inserted as the next sibling of the first array element (parent-1)"
  }
]

The following code is the current method used to merge the arrays:

const c = [
  ...a.filter(i => !b.some(j => j.key===i.key)),
  ...b.map(i => ({...a.find(j => j.key===i.key) ?? {}, ...i}))
]
console.log(c)

The expected outcome of the merge is shown below:

c = [
    {
    "key": "parent-1",
    "type": "parent",
    "items": [
        {
        "key": "parent-1-1",
        "type": "parent",
        "items": [
            {
                "key": "child-1-1",
                "dataType": "text",
                "description": "bar",
                "someproperty": "stays"
            }
        ]
        },
        {
        "key": "parent-1-2",
        "type": "parent",
        "items": [
            {
            "key": "child-1-2",
            "dataType": "text"
            }
        ]
        }
    ]   
    },
    {
        "key": "child-2",
        "dataType": "text",
        "description": "As this does not appear in A, it will be inserted as the next sibling of the first array element (parent-1)"
    }
]

Answers(2)

Tolerim

a month ago

One possible solution for this problem is to use a recursive function that traverses both arrays and performs the merge operation based on the matching keys. Here's an implementation that achieves the desired result:

function mergeArrays(a, b) {
  const result = [];
  
  function mergeObject(aObj, bObj) {
    if (!bObj) {
      // bObj does not exist, so keep aObj
      result.push(aObj);
    } else if (!aObj) {
      // aObj does not exist, so add bObj to result
      result.push(bObj);
    } else if (aObj.key !== bObj.key) {
      // keys don't match, so keep aObj and try next
      result.push(aObj);
      mergeArray(aObj.items, b);
    } else {
      // keys match, so merge aObj and bObj
      const mergedObj = { ...aObj, ...bObj };
      if (aObj.items && bObj.items) {
        // both have nested items, so merge them recursively
        mergedObj.items = mergeArrays(aObj.items, bObj.items);
      }
      result.push(mergedObj);
      mergeArray(aObj.items, b);
    }
  }
  
  function mergeArray(aArr, bArr) {
    bArr.forEach(bObj => {
      const aObj = aArr.find(a => a.key === bObj.key);
      mergeObject(aObj, bObj);
    });
  }
  
  mergeArray(a, b);
  return result;
}

const c = mergeArrays(a, b);
console.log(c);

The mergeArrays function takes two arrays a and b and returns a new merged array c. The mergeObject function takes two objects aObj and bObj and merges them into a new object mergedObj. If either object is missing, it is replaced by the other object. If the keys match, the properties of bObj overwrite the properties of aObj. If both objects have nested items, they are merged recursively using another call to mergeArrays. The mergeArray function performs the merge operation on an array level, calling mergeObject for each pair of objects. With this solution, complex objects with nested children can be properly merged and the desired result can be achieved.

Accepted Answer

Hello! I see that you have two arrays A and B that contain objects. To merge B into A, the following requirements should be met: - If a member of B exists in A, the A object needs to be replaced in place with the B object. However, all properties from the A object should be retained, overwriting any matching properties with the properties of the B object. - If a member of B does not exist in A, it needs to be added to the array as a sibling of the first object in A. It's important to note that the above approach only works for linear objects and breaks down when objects have children. A better approach is required to work with complex objects. The expected outcome of the merge is shown below:

c = [
    {
    "key": "parent-1",
    "type": "parent",
    "items": [
        {
        "key": "parent-1-1",
        "type": "parent",
        "items": [
            {
                "key": "child-1-1",
                "dataType": "text",
                "description": "bar",
                "someproperty": "stays"
            }
        ]
        },
        {
        "key": "parent-1-2",
        "type": "parent",
        "items": [
            {
            "key": "child-1-2",
            "dataType": "text"
            }
        ]
        }
    ]   
    },
    {
        "key": "child-2",
        "dataType": "text",
        "description": "As this does not appear in A, it will be inserted as the next sibling of the first array element (parent-1)"
    }
]

Here's the code that can be used to merge the arrays:

const c = [
  ...a.filter(i => !b.some(j => j.key===i.key)),
  ...b.map(i => ({...a.find(j => j.key===i.key) ?? {}, ...i}))
]
console.log(c)

Let me know if you have any questions or if there's anything else I can help you with!