How to filter array with other array

Question

I have two array, One of them is like this:

 const array1 =  [
      Object {
        "ItemId": 1,
        
      },
      Object {
        "ItemId": 2,
        
      },
    ]

other array is :

     const array2 = [
      Object {
        "obj1": Object {
    
          "Id": 4736,
    
        },
        "obj2": Object {
    
          "ItemId": 1,
     
        },
      }
]

I want to get items in array1, which are not equals in obj2 of array2 .

I tried this but doesnt work

array1.filter(function (item) {
        return array2.map((x) => {
          return x.obj2 != item;
        });

array2 Isn't a valid array? Did something go wrong when copy/pasting? — MaartenDev
– MaartenDev, Commented Mar 5, 2021 at 9:40
There are three issues that immediately catch my eye: 1. array1.filter is expecting a truthy value and array2.map is always returning an array. In this case it will always be truthy. 2. array2.map is just creating a new array with the results of the callback function (x.obj2 != item). This will return an array filled with boolean values. [true, false, true] 3. The comparison looks off to me. Are both objects (item and x.obj) referring to the same object reference? If not, you might rather compare item.ItemId with obj2.ItemId. — webwelten
– webwelten, Commented Mar 5, 2021 at 9:44
@webwelten u are right it return boolean. It is my mistake. Actually I want to get object. and also they referring same object. i can filter with ItemId as well — rnn
– rnn, Commented Mar 5, 2021 at 10:03

webwelten · Accepted Answer · 2021-03-05 10:18:00Z

1

instead of array2.map, you're looking for Array.protype.some or Array.prototype.every. Why?

array1.filter is expecting a truthy value for every item.

array2.map is returning an array (!) with the results of its callback. In your case it's the result of each comparisson x.obj2 != item. It could look something like this: [true, false]. But this array will always evaluate to true.

array2.some() or array2.every() also iterate over the array but will return a boolean for the condition you're using. You can try for yourself and check the code sample afterwards.

 const array1 =  [
  {
    "ItemId": 1,
  },
  {
    "ItemId": 2,
  },
];
    
const array2 = [
  {
    "obj1": {
      "ItemId": 4736,
    },
    "obj2": {
      "ItemId": 1,
    },
  },
];

// errornous filter usage
const test = array1.filter(item => {
  const arr = array2.map(x => x.obj2 !== item); 
  return arr;
});

// suggestion
const filteredResult = array1.filter(item => {
  // both ways work
  // return array2.every(x => x.obj2.ItemId !== item.ItemId); 
  return !array2.some(x => x.obj2.ItemId === item.ItemId); 
  });

console.log('initial result', test);
console.log('correct result', filteredResult);

edited Mar 5, 2021 at 10:18

answered Mar 5, 2021 at 10:04

webwelten

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2 Comments

rnn Over a year ago

I answered your question above

rnn Over a year ago

oh it almost work ! actually it works however when array2 has no item it returns an error just

Cognisun Inc · Accepted Answer · 2021-03-05 09:40:36Z

0

Try this

array1=array1.filter((item) => {
    return array2[0].obj2.ItemId !== item.ItemId;
})

answered Mar 5, 2021 at 9:40

Cognisun Inc

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1 Comment

rnn Over a year ago

how can i handle if array2 has more object ?

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