Difference (upon custom attributes) between two arrays having partial similar objects i.e a-b

Question

How to find difference between two JavaScript arrays having partial similar objects?

Diff = A minus B

const firstList = [{ key: "aa", name:"a" }, { key: "bb", name:"b" }, { key: "cc", name:"c" }];
const secondList = [{ key: "dd", id: 1 }, { key: "cc", id: 2 }];

I want something like const diff = firstList - secondList;

In this case diff needs to hold [ { key: 'aa', name: 'a' }, { key: 'bb', name: 'b' } ]

You could use lodash's without https://lodash.com/docs/4.17.15#without — MoxxiManagarm, Sep 23 '20 at 11:50

Dürrani · Accepted Answer · 2020-09-23T13:46:16.093

1

const firstList = [{ key: "aa", name:"a" }, { key: "bb", name:"b" }, { key: "cc", name:"c" }];
const secondList = [{ key: "dd", id: 1 }, { key: "cc", id: 2 }];

const diff = firstList.filter((first) => {
  return !secondList.some((second) => second.key === first.key);
});

diff; // [ { key: 'aa', name: 'a' }, { key: 'bb', name: 'b' } ]

edited Sep 23 '20 at 13:46

answered Sep 23 '20 at 11:42

Dürrani

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2

This works. But consider replacing the inner `.filter` with `.some`, which feels more natural than using a `filter` and comparing length to 0. Eg: `return !secondList.some(second => second.key === first.key)`. – CRice Sep 23 '20 at 11:46

score 0 · Answer 2 · answered Sep 23 '20 at 11:48

You could take a Set for the second array and filter the first array for excluding elements with same key of the second array.

const
    firstList = [{ key: "aa" }, { key: "bb" }, { key: "cc" }],
    secondList = [{ key: "dd" }, { key: "cc" }],
    keys = new Set(secondList.map(({ key }) => key)),
    result = firstList.filter(({ key }) => !keys.has(key));

console.log(result);

Difference (upon custom attributes) between two arrays having partial similar objects i.e a-b

2 Answers2