如何从特定数组中获取新数组

Question

How do I get a new array from a specific array?

I don't known how to handle an Array like this:

let arr1 = [
  {name: 'a', age: 1},
  {name: 'a', age: 2},
  {name: 'a', age: 3},
  {name: 'b', age: 1},
  {name: 'b', age: 2}
  {name: 'b', age: 3}
  {name: 'c', age: 1}
  {name: 'c', age: 2}
  ...
]

"I want this result: from each item with the same name , pick biggest age value"

let arr2 = [
  {name: 'a', age: 3},
  {name: 'b', age: 3},
  {name: 'c', age: 2} 
  ...
]

Answer 1

Just use filter to select all items with the highest age for their name .

 let arr1 = [{name:'a',age:1},{name:'a',age:2},{name:'a',age:3},{name:'b',age:1},{name:'b',age:2},{name:'b',age:3}]; const biggest = arr1.reduce((a, { name, age }) => { a[name] = a[name] || age; age > a[name] ? a[name] = age : a[name]; return a; }, {}); let arr2 = arr1.filter(({ name, age }) => biggest[name] == age); console.log(arr2); 

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Answer 2

You can use a combination of reduce and Object.values

  const arr1 = [ {name: 'a', age: 1}, {name: 'a', age: 2}, {name: 'a', age: 3}, {name: 'b', age: 1}, {name: 'b', age: 2}, {name: 'b', age: 3}, {name: 'c', age: 1}, {name: 'c', age: 2}, ] const maxNames = arr1.reduce((maxNamesObject, item) => { const { name, age } = item const maxItem = maxNamesObject[name] if (!maxItem || age > maxItem.age) { maxNamesObject[name] = item } return maxNamesObject }, {}) const output = Object.values(maxNames) console.log(output) 

Answer 3

Extracted from this answer: How to filter object array based on attributes?

You can use the Array.prototype.filter method:

let arr2 = arr1.filter(function (obj) {
  return obj.age === 3;
});

Answer 4

This is a more beautiful solution:

 let arr1 = [ {name: 'a', age: 1}, {name: 'a', age: 2}, {name: 'a', age: 3}, {name: 'b', age: 1}, {name: 'b', age: 2}, {name: 'b', age: 3}, {name: 'c', age: 1}, {name: 'c', age: 2}, ] arr2 = Array.from(new Set(arr1.map(e => e.name))).map(e => { return { name: e, age: Math.max(...arr1.filter(ee => ee.name == e).map(ee => ee.age)) } }) console.log(arr2) 

Blockquote

Answer 5

my solution:

 const arr1 = [ {name: 'a', age: 1}, {name: 'a', age: 2}, {name: 'a', age: 3}, {name: 'b', age: 1}, {name: 'b', age: 2}, {name: 'b', age: 3}, {name: 'c', age: 1}, {name: 'c', age: 2}, ] let arr2 = arr1.reduce((acc, item) => { let objectExists = acc.find(e => e.name === item.name) if (!objectExists) acc.push(item) else if (objectExists.age < item.age) { acc[acc.indexOf(objectExists)].age = item.age } return acc }, []) console.log(arr2) 

Answer 6

I didn't notice you update the question. This is not the most pro code.

  let arr1 = [ {name: 'a', age: 1}, {name: 'a', age: 2}, {name: 'a', age: 3}, {name: 'b', age: 1}, {name: 'b', age: 2}, {name: 'b', age: 3}, {name: 'c', age: 1}, {name: 'c', age: 2} ]; let names = []; let output = []; for(obj of arr1){ if (!names.includes(obj.name)) names.push(obj.name); } for(obj of names){ let current = arr1.filter(x => x.name === obj) .reduce((a,b) => a.age > b.age ? a : b); output.push(current); } console.log(output);