How to check if there is an item in an array that exists in another array?

Question

I have the following React code that I want to use to disable a button:

todos.filter(todo => todo.completed === true)
  .map(todo => todo.id)
  .includes(this.state.checkedIds)

My problem is it always returns false. I want to compare two arrays here. If there is an item present in both arrays of this.state.checkedIds and todo.ids it should return true or else false.

The argument that you pass to `includes(...)` (`this.state.checkedIds`) sounds like an array. `includes(...)` checks if an array contains a element not if it contains all the elements of another array. — Titus, Jun 07 '17 at 17:54
Possible duplicate of [Finding matches between multiple JavaScript Arrays](https://stackoverflow.com/questions/11076067/finding-matches-between-multiple-javascript-arrays) — J__, Jun 07 '17 at 17:55
if you click and read it, you'll see that the question and the solution do not reference jquery at all, it only has the tag for some weird reason — J__, Jun 07 '17 at 18:00

score 1 · Answer 1 · answered Jun 07 '17 at 17:54

1

Make checkedIds into a set and then compare them.

var checkedIds = new Set(this.state.checkedIds)
todos.filter( todo => todo.completed === true )
  .map( todo => todo.id )
  .filter( id => checkedIds.has(id) )

answered Jun 07 '17 at 17:54

Alejandro C.

3,771
15
18

score 1 · Answer 2 · answered Jun 07 '17 at 18:25

You can boil it down even further to the following, assuming todo.completed returns a boolean.

Of course, replace the checkedIds with this.state.checkedIds.

const todos = [
  { id: 1, completed: true },
  { id: 2, completed: false },
  { id: 3, completed: true },
  { id: 4, completed: false }
];

const checkedIds = [1, 2, 4, 5];

const results = todos
  .filter(todo => todo.completed)
  .map(todo => checkedIds.includes(todo.id));

console.log(results);

score 1 · Answer 3 · answered Jun 07 '17 at 18:30

You can use include in combination with some for succinctness

var arr1=[1,2,3,4,5,6,7];

var arr2=[8,9,10];

var arr3=[2,1,3,4,5,6,7];
  
if(arr1.some((x)=> arr2.includes(x))){
console.log('true');
//do something
}else{
console.log(false);
//do something
};

if(arr1.some((x)=> arr3.includes(x))){
console.log('true');
//do something
}else{
console.log(false);
//do something
};

// something even shorter would be 
arr1.some((x)=> arr2.includes(x))?console.log(true):console.log(false)

score 0 · Accepted Answer · answered Jun 07 '17 at 18:02

You can just use a simple loop for this:

function arraysIntersect(arr1, arr2) {
    for (var i = 0; i < arr1.length; ++i) {
        if (arr2.includes(arr1[i])) return true;
    }
    return false;
}

I assume state.checkedIds is an array. If that's true, your code doesn't work because you are checking whether your filtered and mapped todos include checkedIds (which it doesn't) instead of checking whether it includes any of the elements of the array checkedIds (which it might).

You can use my code like this:

var doneTodoIds = todos.filter(todo => todo.completed === true ).map( todo => todo.id).includes(this.state.checkedIds);
var result = arraysIntersect(doneTodoIds, this.state.checkedIds);

You could also solve this with a higher level data structure (Alejandro's suggestion), but that might not be necessary (depending on the context of your code fragment).

How to check if there is an item in an array that exists in another array?

4 Answers4