I'm trying to make an array with only values that are not contained in the other array (non-re-CodePudding

I have an array of available users that can be invited and also another array with all joined users to the particular chat. I need to check which of the available users have joined the chat and should be listed elsewhere.

Finally, I want to get an array with only the available users who have not joined the chat.

let availablеUsers = [{id:1,name:'Dani'}, {id:2,name:'Ani'}, {id:3,name:'Marta'}] 
let allUsers = [{id:2,name:'Ani'},{id:10,name:'John'}, {id:3,name:'Marta'}]

The first thing I try to do is find those who are already participating in the chat:

 let joinedUsers = availablеUsers.map((user) => {
    return allUsers?.find((u) => u.id === user.id);
  });

And i get this : [undefined, {… Аni}, {… Marta}]

Then I try to filter the array of available users so that I remove from it those that are in the newly created array and here's the problem I don't know how to do this :/

My idea is something like that:

availablеUsers = availablеUsers.filter((user) => {
    //HERE I don't know what logic to write 
    return joinedUsers?.map((m) => m?.id !== user.id); // this doesn't work, just an example
  });

My goal is to have only those users not contained in the other remain in the availableUsers array.

In the example I have given at the end in the array should remain only {id:1,name:'Dani'}

I welcome any suggestions. If it can do it with chaining, without the extra variable for joinedUsers it would be even better!

CodePudding user response：

There's no need for joinedUsers. Just use find() or some() in the filter() callback, and invert the test.

availableUsers = availableUsers.filter(user => !allUsers.some(u => u.id == user.id))

CodePudding user response：

if users are uniquely identified by id you can use just a filter with a Set of known users:

let availablеUsers = [{id:1,name:'Dani'}, {id:2,name:'Ani'}, {id:3,name:'Marta'}] 
let allUsers = [{id:2,name:'Ani'},{id:10,name:'John'}, {id:3,name:'Marta'}]

let joinedUsers = availablеUsers.filter(
  function ({id}) {
    return this.has(id);
  },
  new Set(allUsers.map(({id}) => id))
);

Accordingly, you can use the same to update availablеUsers in one go:

availablеUsers = availablеUsers.filter(
  function ({id}) {
    return !this.has(id);
  },
  new Set(allUsers.map(({id}) => id))
);

it's not super clear why or when you need !== vs === but the concept is: use a set and use filter instead of map when you want to filter a Set works harder while constructed but it's blazing fast while used via has()