Build array from nested array

Question

i have an array like this :

const toto = [{ id: 1, arrays: [{ id: 1, name: 'tatat' }, { id: 2, name: 'tutu' }] };

And i'd like to get :

[{ id: 1, arrays: [{ id: 1, name: 'tatat' }] }, { id: 1, arrays: [{ id: 2, name: 'tutu' }] }];

This is what i did :

const aEvt = [];
this.organization.events.forEach(x => {
  const e = Object.assign({}, x);
  if (x.eventToOrganizators.length > 1) {
    x.eventToOrganizators.forEach(y => {
      console.log('y', y);
      e.eventToOrganizators = [y];
      console.log('e', e.eventToOrganizators[0]); // OK get the good value
      aEvt.push(e);
    });
  } else {
    aEvt.push(e);
  }
});
console.log(aEvt); // NOT OK, e.eventToOrganizators[0] has all the time the same value

Nina Scholz · Accepted Answer · 2020-10-03 10:52:21Z

1

You could take Array#flatMap for the outer and Array#map for the nested array.

const 
    data = [{ id: 1, arrays: [{ id: 1, name: 'tatat' }, { id: 2, name: 'tutu' }] }],
    result = data.flatMap(({ arrays, ...o }) =>
        arrays.map(item => ({ ...o, arrays: [item] }))
    );

console.log(result);

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

answered Oct 3, 2020 at 10:52

Nina Scholz

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1 Comment

Julien d'Adhemar Over a year ago

Works like a charm, but didn't understand why my ugly solutions didn't works.

Titus · Accepted Answer · 2020-10-03 10:48:28Z

1

You can do something like this:

const toto = [{
  id: 1,
  arrays: [{
    id: 1,
    name: 'tatat'
  }, {
    id: 2,
    name: 'tutu'
  }]
}];

const result = toto.reduce((a, c) => {
  const elements = c.arrays.map(e => ({
    ...c,
    arrays: [e]
  }));
  return [...a, ...elements];
}, []);

console.log(result);

answered Oct 3, 2020 at 10:48

Titus

22.6k1 gold badge26 silver badges36 bronze badges

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