Check if first array's item is in second array-CodePudding

I am building a simple react app and I am kind of stuck on a problem.

What I am trying to do :-

I am trying to check if firstArray's (separate dict inside) item is in secondArray and when I run the loop then checking if is working fine But I am also trying to get item which is not in the array. But it is showing unexpected results in else statement.

I have tried many times with creating different array every time but it is showing same strange results in else statement.

App.js

class App extends React.Component {

   const firstArray = [
    {
      "name" : "Blog 1"
    },
    {
      "name" : "Blog 2"
    },
   ]   

   const secondArray = [
    {
      "name" : "Blog 1"
    },
    {
      "name" : "Blog 2"
    },
    {
      "name" : "Blog 3"
    },
    {
      "name" : "Blog 4"
    },
   ]

  for (var k = 0; k < firstArray.length; k  ) {
    for (var l = 0; l < secondArray.length; l  ) {
      if (secondArray[l].name === firstArray[k].name) {
        // Getting items which are in the same array
        console.log(secondArray[l].name)
      } 
      else {
        // Getting items which are not in array
        console.log(secondArray[l])
      }
    }
  }

   render() {
       return (
          <div>Check below</div>
       )
   }
}

When I try to run the above code then it is showing,

console.log. In if statement statement

{name: 'Blog 1'}
{name: 'Blog 2'}

console.log. In else statement statement It is showing strange results. And I am trying to get results which are not in the first array

{name: 'Blog 1'}
{name: 'Blog 2'}
{name: 'Blog 3'}
{name: 'Blog 1'}
{name: 'Blog 2'}
{name: 'Blog 3'}
{name: 'Blog 1'}
{name: 'Blog 2'}
{name: 'Blog 3'}
{name: 'Blog 1'}
{name: 'Blog 2'}
{name: 'Blog 3'}

I have no idea why it is showing that result but it is showing this for hours.

CodePudding user response：

To determine if the item in the 2nd array is in the 1st array or not you can use a flag. Set it false before inner for and then true if the item exists. Finally check it after inner for.

 for (var k = 0; k < secondArray.length; k  ) {
    var exists = false;
    for (var l = 0; l < firstArray.length; l  ) {
      if (secondArray[k].name === firstArray[l].name) {
        exists = true;
        break;
      } 
    }
    if (exists){
        console.log(secondArray[k].name   " exists");
    } else {
      console.log(secondArray[k].name   " doesn't exist");
    }
 }

CodePudding user response：

Your else statement will work every time when secondArray[k].name === firstArray[l].name is false. Actually you are not checking if secondArray[k] is in first array, but you are checking if it equals to every item in the first array or not.

If I got you right you are trying to do is this:

const commonElements = secondArray.filter(secondElement => 
    firstArray.some(firstElement => firstElement.name === secondElement.name)
)

As a result you will get all elements that appear in both firstArray and secondArray

CodePudding user response：

I'm not really sure what kind of result you are expecting. Here's what I can get.

const firstArray = [{name: "Blog 1"},{name: "Blog 2"}];
const secondArray = [{name: "Blog 1"},{name: "Blog 2"},{name: "Blog 3"},{name: "Blog 4"}];

secondArray.forEach(({ name: second}) => {
    const status = firstArray.some(({ name: first}) => first === second) 
      ? 'exists' 
      : 'does not exist';
      
    console.log(`${second} - ${status} in the first array`);
});

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