Mapping an array to a JavaScript object to get an array of another field

Question

const test_data = [
    {
        _id: '111',
        title: 'Book',
    },
    {
        _id: '222',
        title: 'Cat,
    }
]

I have data that looks like this, and I want to use an array of titles e.g. ['Book', 'Cat'] to retrieve an array of the _ids that match with the title.

From that sample array, I want to retrieve ['111', '222'].

What I've tried was

test_data.filter((item) => { return item.title === "Book" })

But it only retrieves a single object that has Book as the title.

How can I apply this using multiple string values?

Amardeep Bhowmick · Accepted Answer · 2019-09-11 18:56:01Z

1

You can use a Set for you look up table, if the value is present in the set filter the data and map it using the _id:

const test_data = [
    {
        _id: '111',
        title: 'Book',
    },
    {
        _id: '222',
        title: 'Cat',
    }
];

const filterSet = new Set(["Book", "Cat"]);

console.log(test_data.filter(({title}) => filterSet.has(title))
                     .map( ({_id}) => _id));

answered Sep 11, 2019 at 18:56

Amardeep Bhowmick

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2 Comments

Dawn17 Over a year ago

Does this keep the order?

Amardeep Bhowmick Over a year ago

@Dawn17 yes Array.prototype.filter will keep the order, and same for map

Alex Vovchuk · Accepted Answer · 2019-09-11 18:51:00Z

0

for titles:

test_data.map(entry => entry.title);

for ids:

test_data.map(entry => entry.id);

answered Sep 11, 2019 at 18:51

Alex Vovchuk

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Comments

Code Maniac · Accepted Answer · 2019-09-11 18:53:33Z

0

You can use filter and map

const test_data = [{'_id': '111',title: 'Book',},{'_id': '222',title: 'Cat',}]
let conditions = ['Book', 'Cat']

let final = test_data
            .filter(({ title }) => conditions.includes(title))
            .map(({ _id }) => _id)

console.log(final)

answered Sep 11, 2019 at 18:53

Code Maniac

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2 Comments

Dawn17 Over a year ago

Would this actually keep the order too e.g. Book matching with 111?

Code Maniac Over a year ago

@Dawn17 order will depends on your test_data as we are looping on test_data to filter values

Rohith K N · Accepted Answer · 2019-09-11 18:59:07Z

0

I want to use an array of titles e.g. ['Book', 'Cat'] to retrieve an array of the _ids that match with the title.

If you mean to retrieve id using the title, then the following may help you.

const test_data = [
  {
      _id: '111',
      title: 'Book',
  },
  {
      _id: '222',
      title: 'Cat',
  }
]

let new_test_data={};
for(let obj of test_data)
{
  new_test_data[obj.title]=obj._id
}

console.log(new_test_data);//{ Book: '111', Cat: '222' }
console.log(new_test_data["Book"]); //111
console.log(new_test_data["Cat"]); //111

answered Sep 11, 2019 at 18:59

Rohith K N

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