javascript - Finding unique objects in array - Stack Overflow

admin 管理员组

文章数量: 1086019

I have an array as follows:

const arr = [
            {pany: 'a', date: '1'},
            {pany: 'b', date: '1'},
            {pany: 'c', date: '1'},
            {pany: 'a', date: '2'},
            {pany: 'a', date: '1'},
            {pany: 'b', date: '2'},
          ]

I just want to know how to get the unique objects inside it. I tried using lodash with this mand:

uniqBy(arr, 'date');

But it only returns:

[
  {pany: "a", date: "1"},
  {pany: "a", date: "2"}
]

I want something like this one:

[
  {pany: "a", date: "1"},
  {pany: "a", date: "2"},
  {pany: "b", date: "1"},
  {pany: "b", date: "2"},
  {pany: "c", date: "1"},
]

Is there a way in lodash or vanilla JS to have this done?

I have an array as follows:

const arr = [
            {pany: 'a', date: '1'},
            {pany: 'b', date: '1'},
            {pany: 'c', date: '1'},
            {pany: 'a', date: '2'},
            {pany: 'a', date: '1'},
            {pany: 'b', date: '2'},
          ]

I just want to know how to get the unique objects inside it. I tried using lodash with this mand:

uniqBy(arr, 'date');

But it only returns:

[
  {pany: "a", date: "1"},
  {pany: "a", date: "2"}
]

I want something like this one:

[
  {pany: "a", date: "1"},
  {pany: "a", date: "2"},
  {pany: "b", date: "1"},
  {pany: "b", date: "2"},
  {pany: "c", date: "1"},
]

Is there a way in lodash or vanilla JS to have this done?

• javascript
• arrays
• object
• lodash

Share Improve this question Follow edited Jan 29, 2020 at 15:55 Dimitris Papazacharias 69122 gold badges77 silver badges2121 bronze badges asked Jan 27, 2020 at 16:17 Noel RosalesNoel Rosales 6144 bronze badges 2

• group by or .count may help you – Iria Commented Jan 27, 2020 at 16:19
• Your result is not unique by any normal definition, it looks like you've simply reordered the original array – Jamiec Commented Jan 27, 2020 at 16:20

Add a ment  | 

4 Answers 4

Sorted by: Reset to default 7

With help of reduce() in pure js you I created a function which takes an array of objects and array of keys as inputs and return the array which is unique by all those keys.

Following are the steps of the algorithm:

• First we need to create an object using reduce().
• The key of that object will be the values of required keys which are provided each joined by -(I mentioned keyString for each object in the ment of code).
• The object which will have same keyString means same values for given array of keys will automatically occur only once because object can't have duplicate keys
• At last we use Object.values() to to create an array.

const arr = [
            {pany: 'a', date: '1'}, //keyString = "a-1"
            {pany: 'b', date: '1'}, //keyString = "b-1"
            {pany: 'c', date: '1'}, //keyString = "c-1"
            {pany: 'a', date: '2'}, //keyString = "a-2"
            {pany: 'a', date: '1'}, //keyString = "a-1"
            {pany: 'b', date: '2'}, //keyString = "b-2"
            //The item at index 0 and index 4 have same keyString so only a single of them will remain in object.
          ] 

const uniqueBy = (arr, keys) => {
  const obj = arr.reduce((ac, a) => {
    let keyString = keys.map(k => a[k]).join('-');
    ac[keyString] = a;
    return ac;
  }, {});
  return Object.values(obj);
}

console.log(uniqueBy(arr, ['pany', 'date']))

This lodash function bination should do it:

_.uniqWith(arr, _.isEqual);

If you want to consider only a bination of properties for uniqueness and leave other properties out of it, you use uniqBy() with a custom function of your own that sets the criterion. For example:

const arr = [
            {pany: 'a', date: '1', clients: 3},
            {pany: 'b', date: '1', clients: 2},
            {pany: 'c', date: '1', clients: 2},
            {pany: 'a', date: '1', clients: 1}
          ]

const uniqArr = _.uniqBy(arr, function(obj){
  return obj.pany + obj.date;
});

// => [
       {pany: 'a', date: '1', clients: 3},
       {pany: 'b', date: '1', clients: 2},
       {pany: 'c', date: '1', clients: 2}
      ]

In this example, the client property does not affect uniqueness, so the last object will be excluded because the pany and date properties are the same as the first object.

Group them using pany and date fields and use reduce

const arr = [{
    pany: 'a',
    date: '1'
  },
  {
    pany: 'b',
    date: '1'
  },
  {
    pany: 'c',
    date: '1'
  },
  {
    pany: 'a',
    date: '2'
  },
  {
    pany: 'a',
    date: '1'
  },
  {
    pany: 'b',
    date: '2'
  },
];

const res = Object.values(arr.reduce((acc, curr) => {
  const key = ['pany', 'date'].map(x => curr[x]).join('-');

  if (!acc[key]) {
    acc[key] = curr;
  }

  return acc;
}, {}));

console.log(res);

Here with using reduce method in one line.

const arr = [
  { pany: "a", date: "1" },
  { pany: "b", date: "1" },
  { pany: "c", date: "1" },
  { pany: "a", date: "2" },
  { pany: "a", date: "1" },
  { pany: "b", date: "2" }
];

const updated = Object.values(
  arr.reduce(
    (acc, curr) => ({
      ...acc,
      [`${curr.pany}-${curr.date}`]: { ...curr }
    }),
    {}
  )
);

console.log(updated);

本文标签： javascriptFinding unique objects in arrayStack Overflow