比较两个 arrays 并返回对应值

Question

I have 2 arrays of objects:

 const a = [ { name: 'Jack', id: '2' }, { name: 'Jill', id: '25' }, { name: 'Bill', id: '288' } ] const b = [ { title: 'alfa', a_id: '2' }, { title: 'beta', a_id: '25' } ] const test = b.map(i => { a.filter(u => { console.log(u.id === i.a_id) return Object.values(u).includes(i) }) }) console.log(test)

I have to loop trough b , and to check if the a_id corresponds with id from a , to return the name from a that check the condition a_id ==id . How to do this?

at the final i have to get 2 names: Jill and Jack

Answer 1

May not be the most optimal solution. https://jsfiddle.net/5tzqj6ek/

 const a = [ { name: 'Jack', id: '2' }, { name: 'Jill', id: '25' }, { name: 'Bill', id: '288' } ] const b = [ { title: 'alfa', a_id: '2' }, { title: 'beta', a_id: '25' } ] var matchname = []; b.forEach(objb => { a.forEach(obja => { if (objb.a_id === obja.id) { matchname.push(obja.name); } }) }) console.log(matchname);

Answer 2

Maybe that:

 const a = [{ name: 'Jack', id: '2' }, { name: 'Jill', id: '25' }, { name: 'Bill', id: '288' } ] const b = [{ title: 'alfa', a_id: '2' }, { title: 'beta', a_id: '25' } ] const test = b.map(i => { a.map(j => { console.log(j.id === i.a_id? `${j.id} equals ${i.a_id}`: `not equals`) }) })

Answer 3

You can use forEach and find

 const a = [{name: 'Jack',id: '2'},{name: 'Jill',id: '25'},{name: 'Bill',id: '288'}] const b = [{title: 'alfa',a_id: '2'},{title: 'beta',a_id: '25'}] b.forEach(i => { let found = a.find(u => u.id === i.a_id) if (found) { console.log(found.name) } })

Answer 4

Assuming your id s are unique in your a object, you can make a Map from these ids as keys which points to their name value. Then you can .map() your b array to get the value from each a_id by looking it up in the Map using .get() :

 const a = [{ name: 'Jack', id: '2' }, { name: 'Jill', id: '25' }, { name: 'Bill', id: '288' } ]; const b = [{ title: 'alfa', a_id: '2' }, { title: 'beta', a_id: '25' } ]; const idMap = new Map(a.map(({name, id}) => [id, name])); const res = b.map(({a_id}) => idMap.get(a_id)); console.log(res);

If your ids aren't unique, then you can use .reduce() to map to a Map of id: array pairs, where the array portion is the names for each id. Then you can use .flatMap() on the array to map each array to one larger array:

 const a = [{ name: 'Jack', id: '2' }, { name: 'Jill', id: '25' }, { name: 'Bill', id: '288' } ]; const b = [{ title: 'alfa', a_id: '2' }, { title: 'beta', a_id: '25' } ]; const idMap = a.reduce((map, {id, name}) => map.set(id, (map.get(id) || []).concat(name)), new Map); const res = b.flatMap(({a_id}) => idMap.get(a_id)); console.log(res);