Filter nested array for specific value

Question

I have a simple array like this:

const test = [{
  test: 1,
  key: [{
    yes: true,
    no: null
  },{
    yes: true,
    no: null
  },{
    yes: false,
    no: null
  }]
},
{
  test: true,
  key: [{
    yes: true,
    no: null
  }]
},
{
  test: null,
  key: [{
    yes: null,
    no: null
  }]
}
];

And I want to return an array which will only include items where test is truthy (e.g. 1). And the key array inside of test will only include objects with a truthy value for key.yes.

So the expected output is:

[
   {
     test: 1,
     key: [{yes: true, no: null},{yes: true, no: null}]
   },
   {
     test: true,
     key: [{yes: true, no: null}]
   }
];

I tried to achieve this by using a simple filter like this:

const filtered = test.filter(obj => obj.test && obj.key.filter(item => item.yes).length > 0)

but this returns also the values of the key array which are false.

Any ideas why?

do you want a new array with new key array or mutate the old one? — Nina Scholz
– Nina Scholz, Commented Oct 31, 2018 at 12:55
@NinaScholz A new array is perfectly fine which is why I tried using .filter — wasddd_
– wasddd_, Commented Oct 31, 2018 at 12:57

Nina Scholz · Accepted Answer · 2018-10-31 12:59:16Z

2

You need to get a new outer array and new inner arrays, because the outer filtering does not change the inner arrays. If you mutate the inner array and filter the outer array, you mutate the given data.

For getting an independent result, you could check test and if truthy filter key and get a new object for the result set.

var test = [{ test: 1, key: [{ yes: true, no: null }, { yes: true, no: null }, { yes: false, no: null }] }, { test: true, key: [{ yes: true, no: null }] }, { test: null, key: [{ yes: null, no: null }] }],
    result = test.reduce((r, { test, key }) => {
        if (test) {
            r.push({ test, key: key.filter(({ yes }) => yes) });
        }
        return r;
    }, []);

console.log(result);

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

answered Oct 31, 2018 at 12:59

Nina Scholz

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Explosion Pills · Accepted Answer · 2018-10-31 12:59:07Z

0

You will have to filter each individual key array as well.

// array where `test` is truthy
const filtered = test.filter(({ test }) => !!test);

// array where sub-arrays are filterd
const final = filtered.map(({ key }) => key.filter(({ yes }) => !!yes));

answered Oct 31, 2018 at 12:59

Explosion Pills

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Grzesiek Danowski · Accepted Answer · 2018-10-31 13:01:47Z

0

You should first filter main array and then remap to new filtering subbarray, for example:

const filtered = test
   .filter(obj => obj.test && obj.key.some(item => item.yes))
   .map(d => {d.test, key: d.key.filter(item => item.yes));

Or probably filter array by key.yes a moment later:

const filtered = test
   .filter(obj => obj.test)
   .map(d => {d.test, key = d.key.filter(item => item.yes))
   .filter(s => s.key);

answered Oct 31, 2018 at 13:01

Grzesiek Danowski

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