I have two arrays, first containing objects and second containing ids. I want to return a new array from the first array that has ids from the first array. What is the best and efficient way to do this?
const firstArr = [{id: 1, city: London}, {id: 5, city: 'Berlin'}, {id: 10, city: 'Paris'}, {id: 2, city: 'Rome'}]
const secondArr = ['2', '5']
const wantedArr = [{id: 2, city: 'Rome'}, {id: 5, city: 'Berlin'}]
For linear time-complexity convert second array in to set and then use Set.prototype.has
const firstArr = [{id: 1, city: 'London'}, {id: 5, city: 'Berlin'}, {id: 10, city: 'Paris'}, {id: 2, city: 'Rome'}]
const secondArr = ['2', '5'];
let set = new Set(secondArr);
const res = firstArr.filter(x => set.has(String(x.id)));
console.log(res)If you want to keep the order of result array according to the secondArr then first make a object from firstArr and then use map() on secondArr
const firstArr = [{id: 1, city: 'London'}, {id: 5, city: 'Berlin'}, {id: 10, city: 'Paris'}, {id: 2, city: 'Rome'}]
const secondArr = ['2', '5'];
const obj = firstArr.reduce((ac,a) => (ac[a.id] = a,ac), {});
const res = secondArr.map(x => obj[x]);
console.log(res)This should do the trick:
secondArr.map(e => firstArr.filter(a => a.id == +e))
I'm using +e to cast the string to an int, might not be the best way but certainly the shortest.
You can achieve this with .indexOf() or .includes() method
const firstArr = [{ id: 2, city: 'London' }, { id: 2, city: 'Tokyo' }, { id: 5, city: 'Berlin' }, { id: 10, city: 'Paris' }, { id: 6, city: 'Rome' }];
const secondArr = ['2', '5'];
const output = firstArr.filter((r) => {
return secondArr.includes(`${r.id}`);
});
console.log(output);const firstArr = [{ id: 2, city: 'London' }, { id: 2, city: 'Tokyo' }, { id: 5, city: 'Berlin' }, { id: 10, city: 'Paris' }, { id: 6, city: 'Rome' }];
const secondArr = ['2', '5'];
const output = firstArr.filter((r) => {
return secondArr.indexOf(`${r.id}`) > -1;
});
console.log(output);
const wantedArr = firstArr.filter(({ id }) => secondArr.includes(`${id}`));
