Javascript-从对象数组中获取数据

Question

I got this sample data.

"array" : [
    {"Id" : "1", "preferred" : false}, 
    {"Id" : "1", "preferred" : true }, 
    {"Id" : "2", "preferred" : false}, 
    {"Id" : "2", "preferred" : false},]

And i would like to get out of it something like this.

"array2":[{"Id": 1, numOfTrue: 1, numOfFalse: 1},{"Id": 2, numOfTrue: 0, numOfFalse: 2}]

What i got so far is a way how to get unique id form initial array.

const unique = [...new Set(array.map(item => Id))];

Next step would be some forEach over array and comparing Id values and setting some counters for that boolean value. So before i dive into forEach solution i would like to ask if there is another way with using . filter() and .reduce() methods.

Answer 1

You can use reduce() to build a grouping object keyed to Id . Each time you see that Id again increment the value at the appropriate key. In the end your array will be the Object.values() of the object:

 let array = [ {"Id" : "1", "preferred" : false}, {"Id" : "1", "preferred" : true }, {"Id" : "2", "preferred" : false}, {"Id" : "2", "preferred" : false} ] let counts = array.reduce((counts, {Id, preferred}) => { // If you haven't seen this Id yet, make a new entry if (!counts[Id]) counts[Id] = {Id, numOfTrue: 0, numOfFalse: 0} // increment the appropriate value: if (preferred) counts[Id].numOfTrue++ else counts[Id].numOfFalse++ return counts }, {}) // get the values array of the object: console.log(Object.values(counts))