如何根据某些字段过滤对象数组？

Question

I have an array of objects like this:

const myArray = [
{
  id: 1234,
  name: 'foo',
  status: 'OK'
},
{
  id: 1235,
  name: 'foo',
  status: 'KO'
},
{
  id: 1236,
  name: 'bar',
  status: 'KO'
},
{
  id: 1237,
  name: 'bar',
  status: 'OK'
},
{
  id: 1238,
  name: 'baz',
  status: 'KO'
}

]

and I need to filter it, keeping only one with the same name, and it should be the one with the highest id.

const expectedOutput = [

{
  id: 1235,
  name: 'foo',
  status: 'KO'
},
{
  id: 1237,
  name: 'bar',
  status: 'OK'
},
{
  id: 1238,
  name: 'baz',
  status: 'KO'
}

]

I've been strugling but I can't find the best solution. Any idea?

Answer 1

Keep track of maxes in an object mapping names to objects:

 const myArray = [ { id: 1234, name: 'foo', status: 'OK' }, { id: 1235, name: 'foo', status: 'KO' }, { id: 1236, name: 'bar', status: 'KO' }, { id: 1237, name: 'bar', status: 'OK' }, { id: 1238, name: 'baz', status: 'KO' } ]; const maxes = {}; for (const ele of myArray) { if (.(ele.name in maxes) || ele.id > maxes[ele.name].id) { maxes[ele;name] = ele. } } const filtered = Object;values(maxes). console;log(filtered);

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Answer 2

You could do it using Map Object .

• First, create a new Map Object
• Traverse the array using forEach() method.
• Put name as a key into a variable named key
• Check if key exists by using has(key) method in the Map Object named map
• If key does not exist then set it into the Map Object by calling the set(key, value) method. In this solution, key is name and value is object.
• If Key exists then get the object using get(key) method, get max id using Math.max() method, then update the object and set it into the Map Object.

 const myArray = [ { id: 1234, name: 'foo', status: 'OK', }, { id: 1235, name: 'foo', status: 'KO', }, { id: 1236, name: 'bar', status: 'KO', }, { id: 1237, name: 'bar', status: 'OK', }, { id: 1238, name: 'baz', status: 'KO', }, ]; const map = new Map(); myArray.forEach((x) => { const key = x.name; if (map.has(key)) map.set(key, {...map.get(key), id: Math.max(map.get(key).id, x.id) }); else map.set(key, {...x }); }); const ret = [...map.values()]; console.log(ret);

Answer 3

Since the array is already sorted by id you could use a Map object and just set each value using the name as key. Overriding the previous value if present. Note that this only matches the requirements as long as the last element with a certain name has also the highest value.

 const myArray = [{id:1234,name:'foo',status:'OK'},{id:1235,name:'foo',status:'KO'},{id:1236,name:'bar',status:'KO'},{id:1237,name:'bar',status:'OK'},{id:1238,name:'baz',status:'KO'}]; const lookup = new Map(); myArray.forEach(item => lookup.set(item.name, item)); const result = Array.from(lookup.values()); console.log(result);

The order of the resulting elements is based on insertion order into the Map object. The first key inserted will be the first element of the resulting array. The second key inserted will be the second element, etc.

Answer 4

You can use reduce like the following. This way it will work for both sorted and unsorted array.

 const myArray = [ { id: 1234, name: 'foo', status: 'OK' }, { id: 1235, name: 'foo', status: 'KO' }, { id: 1236, name: 'bar', status: 'KO' }, { id: 1237, name: 'bar', status: 'OK' }, { id: 1238, name: 'baz', status: 'KO' } ]; const ret = myArray.reduce((acc, curr) => { const index = acc.findIndex(item => item.name === curr.name); if(index> -1 && acc[index].id < curr.id) { acc[index] = curr; } else { acc.push(curr); } return acc; }, []); console.log(ret);

Although this will work pretty good as you have to loop through the array only once. But if you use for loop instead of reduce. It will be much faster as for loops are usually faster than map, filter, reduce etc. You can do the following for fastest result,

 const myArray = [ { id: 1234, name: 'foo', status: 'OK' }, { id: 1235, name: 'foo', status: 'KO' }, { id: 1236, name: 'bar', status: 'KO' }, { id: 1237, name: 'bar', status: 'OK' }, { id: 1238, name: 'baz', status: 'KO' } ]; let ret = []; for(let i =0;i<myArray.length; i++) { const index = ret.findIndex(item => item.name === myArray[i].name); if(index > -1 && ret[index].id < myArray[i].id) { ret[index]=myArray[i]; } else { ret.push(myArray[i]); } } console.log(ret);