如何从对象数组返回匹配的属性值

Question

I have below array,

var abc = [
 {name: 'name1', id: '1', value: 1},
 {name: 'name2', id: '2', value: 3},
 {name: 'name3', id: '3', value: 2},
 {name: 'name4', id: '4', value: 2}
];

i want to return,

var abc = [
 {name: 'name3', id: '3', value: 2},
 {name: 'name4', id: '4', value: 2}
];

because both object has a same value. How I can achieve this using lodash or javascript.

Answer 1

You can create an object and its value will an array which will contain only those objects whose value will be same

 var abc = [{ name: 'name1', id: '1', value: 1 }, { name: 'name2', id: '2', value: 3 }, { name: 'name3', id: '3', value: 2 }, { name: 'name4', id: '4', value: 2 } ]; let m = abc.reduce(function(acc, curr) { if (!acc.hasOwnProperty(curr.value)) { acc[curr.value] = []; } acc[curr.value].push(curr) return acc; }, {}) Object.keys(m).forEach(function(item) { if (m[item].length > 1) { console.log(m[item]) } }) 

Answer 2

Use filter and findIndex .

 var abc = [ {name: 'name1', id: '1', value: 1}, {name: 'name2', id: '2', value: 3}, {name: 'name3', id: '3', value: 2}, {name: 'name4', id: '4', value: 2} ]; const res = abc.filter(obj => { return abc.findIndex(obj2 => obj2.id !== obj.id && obj2.value === obj.value) > -1; }); console.log(res); 

Answer 3

You can achieve this using Array.reduce with complexity of O(n)

You can create an object/map with key as value property of the object. For each object in array, check for value in object. If value does not exist add it to map. If the value exists ( duplicate ), then add the object to array along with the value stored in map. You will need to reset the value in map so that you do not end up adding the first value more than once.

 var abc = [{name: 'name1', id: '1', value: 1},{name: 'name2', id: '2', value: 3},{name: 'name3', id: '3', value: 2},{name: 'name4', id: '4', value: 2}]; var obj = {}; var result = abc.reduce((a,c) => { if(obj[c.value]) { if(obj[c.value] !== true) { a.push(obj[c.value]); obj[c.value] = true; } a.push(c); } else obj[c.value] = c; return a; }, []); console.log(result); 

Answer 4

You can group them by the value field using Array.prototype.reduce()

Here is how to do so:

 var abc = [ {name: 'name1', id: '1', value: 1}, {name: 'name2', id: '2', value: 3}, {name: 'name3', id: '3', value: 2}, {name: 'name4', id: '4', value: 2} ]; var reduced = abc.reduce((accumulated, current) => { if(!accumulated[current.value]) { accumulated[current.value] = []; } accumulated[current.value].push(current); return accumulated }, {}) // var value = 1 var value = 2; console.log(reduced[value]) 

Just change the value field to get the required array.

Answer 5

It is interesting that you posted with a lodash tag but got not a single lodash answer.

I would like to add one since it is more concise by simply using the short form of .countBy and .filter :

 var data = [ {name: 'name1', id: '1', value: 1}, {name: 'name2', id: '2', value: 3}, {name: 'name3', id: '3', value: 2}, {name: 'name4', id: '4', value: 2} ]; var result = _.filter(data, ({value}) => _.countBy(data, 'value')[value] > 1) console.log(result) 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.11/lodash.min.js"></script>