Javascript how to compare the first element from array with the other elements

Question

I have an array mainArray that contains n arrays of objects and I need to compare all elements from mainArray to check if the property id from each object exists in the other objects:
- if it is found, then check if the other properties are identical and return the id if they are not identical.
- if at least one of the mainArray[n] does not have an object with that id then return the id.

Here are some examples:
Example 1:

mainArray = [
  [
    {
      "id":"trackingcode",
      "classification":
      [
        {
          "name":"Creative Elements",
          "description":"",
          "type":"text",
          "date_enabled":false
        },
        {
          "name":"Campaigns",
          "description":"",
          "type":"text",
          "date_enabled":true
        }
      ]
    },
    {
      "id":"evar9",
      "classification":
      [
        {
          "name":"Type",
          "description":"",
          "type":"text",
          "date_enabled":false
        },
        {
          "name":"Domain",
          "description":"",
          "type":"text",
          "date_enabled":false,
          "children":
          [
            {
              "name":"sub classification",
              "description":"",
              "type":"text",
              "parent_name":"Domain",
              "date_enabled":false
            }
          ]
        }
      ]
    }
  ],
  [
    {
      "id":"trackingcode",
      "classification":
      [
        {
          "name":"Creative Elements",
          "description":"",
          "type":"text",
          "date_enabled":false
        },
        {
          "name":"Campaigns",
          "description":"",
          "type":"text",
          "date_enabled":true
        }
      ]
    }
  ]
]

mainArray[0] !== mainArray[1] => return ["evar9"]
- mainArray[1] does not have an object with the property "id": "evar9"

Example 2:

mainArray = [
  [
    {
      "id":"evar9",
      "classification":
      [
        {
          "name":"Type",
          "description":"",
          "type":"text",
          "date_enabled":false
        },
        {
          "name":"Domain",
          "description":"",
          "type":"text",
          "date_enabled":false,
          "children":
          [
            {
              "name":"sub classification",
              "description":"",
              "type":"text",
              "parent_name":"Domain",
              "date_enabled":false
            }
          ]
        }
      ]
    }
  ],
  [
    {
      "id":"trackingcode",
      "classification":
      [
        {
          "name":"Creative Elements",
          "description":"",
          "type":"text",
          "date_enabled":false
        },
        {
          "name":"Campaigns",
          "description":"",
          "type":"text",
          "date_enabled":true
        }
      ]
    }
  ],
  [
    {
      "id":"trackingcode",
      "classification":
      [
        {
          "name":"Creative Elements",
          "description":"",
          "type":"text",
          "date_enabled":false
        },
        {
          "name":"Campaigns",
          "description":"",
          "type":"text",
          "date_enabled":true
        }
      ]
    },
    {
      "id":"evar1",
      "classification":
      [
        {
          "name":"Creative",
          "description":"",
          "type":"text",
          "date_enabled":false
        },
        {
          "name":"Variables",
          "description":"",
          "type":"text",
          "date_enabled":true
        }
      ]
    }
  ]
]

return ["trackingcode", "evar1", "evar9"]
- mainArray[0] does not have an object with the property "id": "trackingcode"
- mainArray[0] and mainArray[1] does not have an object with the property "id": "evar1"
- mainArray[1] and mainArray[2] does not have an object with the property "id": "evar9"

Example 3:

mainArray = [
  [
    {
      "id":"trackingcode",
      "classification":
      [
        {
          "name":"Creative Elements",
          "description":"",
          "type":"text",
          "date_enabled":false
        },
        {
          "name":"Campaigns",
          "description":"",
          "type":"text",
          "date_enabled":true
        }
      ]
    },
    {
      "id":"evar9",
      "classification":
      [
        {
          "name":"Type",
          "description":"",
          "type":"text",
          "date_enabled":false
        },
        {
          "name":"Domain",
          "description":"",
          "type":"text",
          "date_enabled":false,
          "children":
          [
            {
              "name":"sub classification",
              "description":"",
              "type":"text",
              "parent_name":"Domain",
              "date_enabled":false
            }
          ]
        }
      ]
    }
  ],
  [
    {
      "id":"trackingcode",
      "classification":
      [
        {
          "name":"Creative Elements",
          "description":"",
          "type":"text",
          "date_enabled":false
        },
        {
          "name":"Campaigns",
          "description":"",
          "type":"text",
          "date_enabled":true
        }
      ]
    },
    {
      "id":"evar9",
      "classification":
      [
        {
          "name":"Type",
          "description":"",
          "type":"text",
          "date_enabled":false
        },
        {
          "name":"Domain",
          "description":"",
          "type":"text",
          "date_enabled":false,
          "children":
          [
            {
              "name":"different name",
              "description":"different description",
              "type":"text",
              "parent_name":"Domain",
              "date_enabled":false
            }
          ]
        }
      ]
    }
  ]
]

return ["evar9"]
- the "children" properties are different

@NinaScholz sorry, I thought that I removed that object. Check now. — Valip
– Valip, Commented Nov 25, 2016 at 10:47

Nina Scholz · Accepted Answer · 2016-11-25 12:18:27Z

You could iterate and count the objects with the same name and make a check if some equal id are found.

This proposal uses JSON.stringify, because I think the data is equal generated and the order of properties is the same.

/**
 * Checks every array for sameness and returns only different id
 *
 * @param {array} array An array with nested arrays with object, with property id
 * @return Difference.
 */
function check(array) {

    // create object without prototypes
    var count = Object.create(null);

    // iterate given array
    array.forEach(function (a, i) {
   
        // and the inner array
        a.forEach(function (b, j) {

            // check if id exist, if not take a new object with count,
            // objects and same for later check
            count[b.id] = count[b.id] || { count: 0, objects: [], same: true };

            // increment count for later check with the length of the given array
            count[b.id].count++;

            // save actual object for check for sameness
            count[b.id].objects.push(b);

            // if count is greater than one, test obejct for equality
            if (count[b.id].count > 1) {

                // assign to property same result of test with serialized objects
                count[b.id].same = count[b.id].same && JSON.stringify(count[b.id].objects[0]) === JSON.stringify(b);
            }
        });
    });

    // get all keys and return only the keys which count is not equal 
    // to the lenght of the given array or which objects are not equal
    return Object.keys(count).filter(function (k) {
        return count[k].count !== array.length || !count[k].same;
    });
}

var mainArray1 = [[{ "id": "trackingcode", "classification": [{ "name": "Creative Elements", "description": "", "type": "text", "date_enabled": false }, { "name": "Campaigns", "description": "", "type": "text", "date_enabled": true }] }, { "id": "evar9", "classification": [{ "name": "Type", "description": "", "type": "text", "date_enabled": false }, { "name": "Domain", "description": "", "type": "text", "date_enabled": false, "children": [{ "name": "sub classification", "description": "", "type": "text", "parent_name": "Domain", "date_enabled": false }] }] }], [{ "id": "trackingcode", "classification": [{ "name": "Creative Elements", "description": "", "type": "text", "date_enabled": false }, { "name": "Campaigns", "description": "", "type": "text", "date_enabled": true }] }]],
    mainArray2 = [[{ "id": "evar9", "classification": [{ "name": "Type", "description": "", "type": "text", "date_enabled": false }, { "name": "Domain", "description": "", "type": "text", "date_enabled": false, "children": [{ "name": "sub classification", "description": "", "type": "text", "parent_name": "Domain", "date_enabled": false }] }] }], [{ "id": "trackingcode", "classification": [{ "name": "Creative Elements", "description": "", "type": "text", "date_enabled": false }, { "name": "Campaigns", "description": "", "type": "text", "date_enabled": true }] }], [{ "id": "trackingcode", "classification": [{ "name": "Creative Elements", "description": "", "type": "text", "date_enabled": false }, { "name": "Campaigns", "description": "", "type": "text", "date_enabled": true }] }, { "id": "evar1", "classification": [{ "name": "Creative", "description": "", "type": "text", "date_enabled": false }, { "name": "Variables", "description": "", "type": "text", "date_enabled": true }] }]],
    mainArray3 = [[{ "id": "trackingcode", "classification": [{ "name": "Creative Elements", "description": "", "type": "text", "date_enabled": false }, { "name": "Campaigns", "description": "", "type": "text", "date_enabled": true }] }, { "id": "evar9", "classification": [{ "name": "Type", "description": "", "type": "text", "date_enabled": false }, { "name": "Domain", "description": "", "type": "text", "date_enabled": false, "children": [{ "name": "sub classification", "description": "", "type": "text", "parent_name": "Domain", "date_enabled": false }] }] }], [{ "id": "trackingcode", "classification": [{ "name": "Creative Elements", "description": "", "type": "text", "date_enabled": false }, { "name": "Campaigns", "description": "", "type": "text", "date_enabled": true }] }, { "id": "evar9", "classification": [{ "name": "Type", "description": "", "type": "text", "date_enabled": false }, { "name": "Domain", "description": "", "type": "text", "date_enabled": false, "children": [{ "name": "different name", "description": "different description", "type": "text", "parent_name": "Domain", "date_enabled": false }] }] }]];

console.log(check(mainArray1));
console.log(check(mainArray2));
console.log(check(mainArray3));

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

This works perfect, thank you! I need to study the code a little to understand what happens there...it would help me a lot if you can add just a couple comments in code...
please see edit, i change the handling form indices to objects.

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