Find the rowIndex and the changed object property while comparing two arrays of objects – Javascript

  Kiến thức lập trình

I have two dynamic arrays of objects which I get from an API (the fields are created by an end user, I am not aware of the keys beforehand). One is original and the other is a modified version. I want to compare them and get the changed rowIndex on the modified one as well as which object properties have been changed. This is my code.

const originalData = [{
  brand: 'Honda',
  model: 'Accord'
}, {
  brand: 'Honda',
  model: 'Civic'
}, {
  brand: 'Toyota',
  model: 'Camry'
}, {
  brand: 'Toyota',
  model: 'Corolla'
}]

const data = [{
  brand: 'Honda',
  model: 'Accord'
}, {
  brand: 'Honda',
  model: 'CRV'
}, {
  brand: 'Toyota',
  model: 'Camry'
}, {
  brand: 'Nissan',
  model: 'RAV4'
}]


console.log(data.reduce((a, c, i, arr) => {
  if (!originalData.some(j => {
      return _.isEqual(c, j)
    })) {
    a.push({
      rowIndex: i,
      changedKeys: arr[i]
    })
  }
  return a
}, []))
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.21/lodash.min.js"></script>

I am not able to get the changedKeys here. I am able to get the object itself. How do I get the changed key?

Expected output:

    [
        {
            "rowIndex": 1,
            "changedKeys": ['model']
        },
        {
            "rowIndex": 3,
            "changedKeys": ['brand', 'model']
        }
    ]

Please advice.

  • javascript
  • arrays

5

Using reduce. Iterate over the array of objects. Initialise an array called changedKeys. Iterate over the keys/values in each object and if there’s a mismatch, push the key into changedKeys. Finally, if there are keys in changedKeys push that into the accumulator for the next round of iteration.

const originalData=[{brand:"Honda",model:"Accord"},{brand:"Honda",model:"Civic"},{brand:"Toyota",model:"Camry"},{brand:"Toyota",model:"Corolla"},{brand:"Renault",model:"Clio"}],data=[{brand:"Honda",model:"Accord"},{brand:"Honda",model:"CRV"},{brand:"Toyota",model:"Camry"},{brand:"Nissan",model:"Corolla"},{brand:"Datsun",model:"Cherry"}];

const out = originalData.reduce((acc, obj, i) => {
  
  // Initialise `changedKeys`
  const changedKeys = [];
  
  // Loop over the original object and compare the
  // values to those in the new data set, pushing the
  // key into `changedKeys` if there's a mismatch
  for (const key in obj) {
    if (obj[key] !== data[i][key]) {
      changedKeys.push(key);
    }
  }
  
  // If there are mismatches push an object into
  // the accumulator with the index
  if (changedKeys.length) {
    acc.push({ rowIndex: i, changedKeys });
  }
 
  // Return the accumulator for the next iteration
  return acc;

}, []);

console.log(out);

Additional documentation

  • Destructuring assignment

2

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