How to filter keys of an object with lodash?

Question

I have an object with some keys, and I want to only keep some of the keys with their value?

I tried with filter:

const data = {
  aaa: 111,
  abb: 222,
  bbb: 333
};

const result = _.filter(data, (value, key) => key.startsWith("a"));

console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.min.js"></script>

But it prints an array:

[111, 222]

Which is not what I want.

How to do it with lodash? Or something else if lodash is not working?

Answer 1

Lodash has a _.pickBy function which does exactly what you're looking for.

var thing = {
  "a": 123,
  "b": 456,
  "abc": 6789
};

var result = _.pickBy(thing, function(value, key) {
  return _.startsWith(key, "a");
});

console.log(result.abc) // 6789
console.log(result.b)   // undefined

<script src="https://cdn.jsdelivr.net/lodash/4.16.4/lodash.min.js"></script>

Answer 2

Just change filter to omitBy

const data = { aaa: 111, abb: 222, bbb: 333 };
const result = _.omitBy(data, (value, key) => !key.startsWith("a"));
console.log(result);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.min.js"></script>

Answer 3

A non-lodash way to solve this in a fairly readable and efficient manner:

function filterByKeys(obj, keys = []) {
  const filtered = {}
  keys.forEach(key => {
    if (obj.hasOwnProperty(key)) {
      filtered[key] = obj[key]
    }
  })
  return filtered
}

const myObject = {
  a: 1,
  b: 'bananas',
  d: null
}

const result = filterByKeys(myObject, ['a', 'd', 'e'])
console.log(result) // {a: 1, d: null}

Answer 4

Here is an example using lodash 4.x:

const data = {
  aaa: 111,
  abb: 222,
  bbb: 333
};

const result = _.pickBy(data, (value, key) => key.startsWith("a"));

console.log(result);
// Object { aaa: 111, abb: 222 }

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.15/lodash.min.js"></script>
<strong>Open your javascript console to see the output.</strong>

Answer 5

const data = {
  aaa: 111,
  abb: 222,
  bbb: 333
};
const result = Object.keys(data).filter((val) => val.includes("a"));
console.log(result);

Answer 6

Pure JS solution:

const data = {
  aaa: 111,
  abb: 222,
  bbb: 333
};

const result = Object.keys(data).filter( key => {
  return key.indexOf('a') == 0
}).map( key => {
  return { key: data[key] }
})

console.log(result)

1. Filter through the data for keys that starts with the letter 'a'
2. Map those keys with the proper value, and return as key:value object

Answer 7

You can use the _.omit() function.

it accepts the keys to filter as an string array like below:

var object = { a: 1, b: 2, c: 3 }
_.omit(object, ['a', 'c'])
// => { b: 2 }

Answer 8

Native ES2019 one-liner

const data = {
  aaa: 111,
  abb: 222,
  bbb: 333
};

const filteredByKey = Object.fromEntries(Object.entries(data).filter(([key, value]) => key.startsWith("a")))

console.log(filteredByKey);