Fixing object diff algorithm to create arrays instead of objects

Question

I'm trying to build an algorithm which can output the difference between two objects. I can't figure out how to create an array when the typeof object is an array. I know it has to do with the the first key returned when enumerating the array is the index as a string; "0". So it's assigning "0" as an object instead of the array.

    function difference(o1, o2) {

                var k;
                var kDiff;
                var diff = {};

                for (k in o1)
                {
                    if (!o1.hasOwnProperty(k)) { }
                    else if (typeof o1[k] != 'object' || typeof o2[k] != 'object')
                    {
                        if (!(k in o2) || o1[k] !== o2[k]){
                            diff[k] = o2[k];
                        }
                    } else if (kDiff = difference(o1[k], o2[k]))
                    {
                        diff[k] = kDiff;
                    }
                }
                for (k in o2)
                {
                    if (o2.hasOwnProperty(k) && (!o1 || !(k in o1)))
                    {
                        diff[k] = o2[k];
                    }
                }
                for (k in diff)
                {
                    if (diff.hasOwnProperty(k))
                    {
                        return diff;
                    }
                }

                return false;
            }

Test Case

    var lhs = {
        "Id": 1,
        "Type" : "Mortgage",
        "Amount": 500000,
        "Rate" : .045,
        "Borrowers": [
            {
                "Id": 1,
                "FirstName": "Jon",
                "Employment": [
                    {
                        "Id": 1,
                        "Employer": "Walmart",
                        "Income": [
                            {
                                "Id": 1,
                                "MonthlyIncome": 5000,
                                "Type": "Base"
                            },
                            {
                                "Id": 2,
                                "MonthlyIncome": 1000,
                                "Type": "Overtime"
                            }
                        ]
                    }
                ]

            }

        ]
    }
    var rhs = {
        "Id": 1,
        "Type" : "Mortgage",
        "Amount": 500001,
        "Rate" : .045,
        "Borrowers": [
            {
                "Id": 1,
                "FirstName": "Don",
                "Employment": [
                    {
                        "Id": 1,
                        "Employer": "Walmart",
                        "Income": [
                            {
                                "Id": 1,
                                "MonthlyIncome": 5000,
                                "Type": "Base"
                            },
                            {
                                "Id": 2,
                                "MonthlyIncome": 500,
                                "Type": "Other"
                            }
                        ]
                    }
                ]

            }

        ]
    }

    var changes = JSON.stringify(difference(lhs, rhs);

Expected Result:

{
    "Amount": 500001,
    "Borrowers": [
        {
            "FirstName": "Don",
            "Employment": [
                {
                    "Income": [
                        {
                            "MonthlyIncome": 500,
                            "Type": "Other"
                        }
                    ]
                }
            ]
        }
    ]
}

Not:

{
    "Amount": 500001,
    "Borrowers": {
        "0": {
            "FirstName": "Don",
            "Employment": {
                "0": {
                    "Income": {
                        "1": {
                            "MonthlyIncome": 500,
                            "Type": "Other"
                        }
                    }
                }
            }
        }
    }
}

just hints: typeof [] returns 'object' and not 'array' (use Array.isArray instead). Then you define diff = {} so you can't have an array here.. — Kaddath
– Kaddath, Commented Nov 9, 2018 at 14:51

SpeedOfRound · Accepted Answer · 2018-11-09 14:52:39Z

1

I'm a little confused by what you are trying to do, but if lodash is an option to use, does this help?

function difference(base, object) {
  function changes(object, base) {
    return _.transform(object, function(result, value, key) {
      if (!_.isEqual(value, base[key])) {
        result[key] =
          _.isObject(value) && _.isObject(base[key])
            ? changes(value, base[key])
            : value;
      }
    });
  }
  return changes(object, base);
}

answered Nov 9, 2018 at 14:52

SpeedOfRound

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2 Comments

ddrjca Over a year ago

I didn't know about this functionality in lodash. I have another requirement which is to always include the 'Id' field and value, if any of the other field values are changed in an object. Is there a way to this with lodash transform?

Kaddath Over a year ago

@ddrjca you have key and value in function(result, value, key), so yes, you just need to test if key === 'Id' and assign it to result if the case

ddrjca · Accepted Answer · 2018-11-11 15:57:27Z

0

Based the hint from @Kaddath, the returned differences must be defined based on the object type being evaluated:

function difference(o1, o2) {

  var k;
  var kDiff;
  var diff = Array.isArray(o1) ? [] : {};

}

answered Nov 11, 2018 at 15:57

ddrjca

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