Javascript - Check if arrays within an array are the same

PhilippM
June 20, 2023
117 views
0 votes
2 Answers

Whats the best way to check if the arrays within an array are the same in my case?

var arrSession = [
  {
    type: '1',
    usecase: [ '1' ]
  },
  {
    type: '1',
    usecase: [ '1' ]
  }
];

var checkUsecase = arrSession.every(isSame);

function isSame(obj, index, arr) {
    if (index === 0) {
        return true;
    } else {
        return (
            (obj.type === arr[index - 1].type) &&
            (obj.usecase === arr[index - 1].usecase)
        );
    }
}

console.log('checkUsecase:');
console.log(checkUsecase);

The ‘usecase’ object within the array use to be a string ” and the isSame function used to work. But now they are arrays too. How to change the isSame function?

Here is a fiddle: https://jsfiddle.net/3j0odpec/

Answers

First we make some recursive compare function to walk nested arrays/objects. Then we run it over the array comparing that the current item is equal to the previous one.

While it’s a bit slower than comparing JSON.stringified array items of the OP’s data:

It wins with more complex objects:

const arrSession = [
    {
        type: '1',
        usecase: ['1']
    },
    {
        type: '1',
        usecase: ['1']
    }
];

const isSameItems = arrSession.every((item, idx, arr) => idx === 0 || isSame(item, arr[idx - 1]));

console.log('the array has all items the same: ', isSameItems);

function isSame(a, b) {

    const objectCount = [a, b].reduce((sum, item) => sum + (item.__proto__.constructor.name === 'Object' ? 1 : 0), 0);
    const arrayCount = objectCount ? 0 : [a, b].reduce((sum, item) => sum + (Array.isArray(item) ? 1 : 0), 0);

    if (arrayCount === 2 || objectCount === 2) {
        for (const i of arrayCount ? a.keys() : Object.keys(a)) {
            if (!isSame(a[i], b[i])) {
                return false;
            }
        }
        return true;
    }
    
    if (arrayCount || objectCount) {
        return false;
    }

    return a === b;


}

<script benchmark data-count="1">

    const arrSession = Array.from({ length: 300000 }).reduce(arr => arr.push(...[
        {
            type: '1',
            usecase: ['1'],
            child: {
                type: '1',
                usecase: ['1'],
                child: {
                    type: '1',
                    usecase: ['1'],
                    child: {
                        type: '1',
                        usecase: ['1'],
                    }
                }
            },
            child: {
                type: '1',
                usecase: ['1'],
            }
        }
    ]) && arr, []);

    // @benchmark JSON.stringify

    arrSession.every((item, idx, arr) => idx === 0 || JSON.stringify(item) === JSON.stringify(arr[idx - 1]));

    // @benchmark recursive isSame

    arrSession.every((item, idx, arr) => idx === 0 || isSame(item, arr[idx - 1]));

    function isSame(a, b) {

        const objectCount = [a, b].reduce((sum, item) => sum + (item.__proto__.constructor.name === 'Object' ? 1 : 0), 0);
        const arrayCount = objectCount ? 0 : [a, b].reduce((sum, item) => sum + (Array.isArray(item) ? 1 : 0), 0);

        if (arrayCount === 2 || objectCount === 2) {
            for (const i of arrayCount ? a.keys() : Object.keys(a)) {
                if (!isSame(a[i], b[i])) {
                    return false;
                }
            }
            return true;
        }
        
        if (arrayCount || objectCount) {
            return false;
        }

        return a === b;

    }


</script>
<script src="https://cdn.jsdelivr.net/gh/silentmantra/benchmark/loader.js"></script>

For sameness / equality comparison of JSON conform data structures where performance is important as well one might consider the following recursive implementation of isDeepDataStructureEquality …

<script>
  // implemented by Peter Seliger
  function isDeepDataStructureEquality(a, b) {
    let isEqual = Object.is(a, b);

    if (!isEqual) {
      if (Array.isArray(a) && Array.isArray(b)) {

        isEqual = (a.length === b.length) && a.every(
          (item, idx) => isDeepDataStructureEquality(item, b[idx])
        );
      } else if (
        a && b
        && (typeof a === 'object')
        && (typeof b === 'object')
      ) {
        const aKeys = Object.keys(a);
        const bKeys = Object.keys(b);

        isEqual = (aKeys.length === bKeys.length) && aKeys.every(
          (key, idx) => isDeepDataStructureEquality(a[key], b[key])
        );
      }
    }
    return isEqual;
  }
</script>
<script>
  // implemented by Alexander Nenashev
  function isSame(a, b) {
    const objectCount = [a, b].reduce((sum, item) => sum + (item.__proto__.constructor.name === 'Object' ? 1 : 0), 0);
    const arrayCount = objectCount ? 0 : [a, b].reduce((sum, item) => sum + (Array.isArray(item) ? 1 : 0), 0);

    if (arrayCount === 2 || objectCount === 2) {
      for (const i of arrayCount ? a.keys() : Object.keys(a)) {
        if (!isSame(a[i], b[i])) {
          return false;
        }
      }
      return true;
    }
    if (arrayCount || objectCount) {
      return false;
    }
    return a === b;
  }
</script>
<script benchmark data-count="10">

  const arrSession = Array
    .from({ length: 300000 })
    .reduce(arr => arr.push(...[{
      type: '1',
      usecase: ['1'],
      child: {
        type: '1',
        usecase: ['1'],
        child: {
          type: '1',
          usecase: ['1'],
          child: {
            type: '1',
            usecase: ['1'],
          },
        },
      },
      child: {
        type: '1',
        usecase: ['1'],
      }
    }]) && arr, []);

    // countercheck implementations with an unequal data structure.
    // arrSession.at(-1).child.usecase[0] = 0;

    // @benchmark JSON.stringify
    arrSession.every((item, idx, arr) =>
      idx === 0 || JSON.stringify(item) === JSON.stringify(arr[idx - 1])
    );
    // @benchmark recursive isSame
    arrSession.every((item, idx, arr) =>
      idx === 0 || isSame(item, arr[idx - 1])
    );
    // @benchmark recursive isDeepDataStructureEquality
    arrSession.every((item, idx, arr) =>
      idx === 0 || isDeepDataStructureEquality(item, arr[idx - 1])
    );
</script>
<script src="https://cdn.jsdelivr.net/gh/silentmantra/benchmark/loader.js"></script>

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Javascript – Check if arrays within an array are the same

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