How can an array be grouped by two properties?

Question

Ex:

const arr = [{
  group: 1,
  question: {
    templateId: 100
  }
}, {
  group: 2,
  question: {
    templateId: 200
  }
}, {
  group: 1,         


        

Answer 1

@Bergi's answer is great if you can hard-code the inputs.

If you want to use string inputs instead, you can use the sort() method, and walk the objects as needed.

This solution will handle any number of arguments:

function groupBy(arr) {
  var arg = arguments;
  
  return arr.sort((a, b) => {
    var i, key, aval, bval;
    
    for(i = 1 ; i < arguments.length ; i++) {
      key = arguments[i].split('.');
      aval = a[key[0]];
      bval = b[key[0]];
      key.shift();
      while(key.length) {  //walk the objects
        aval = aval[key[0]];
        bval = bval[key[0]];
        key.shift();
      };
      if     (aval < bval) return -1;
      else if(aval > bval) return  1;
    }
    return 0;
  });
}

const arr = [{
  group: 1,
  question: {
    templateId: 100
  }
}, {
  group: 2,
  question: {
    templateId: 200
  }
}, {
  group: 1,
  question: {
    templateId: 100
  }
}, {
  group: 1,
  question: {
    templateId: 300
  }
}];

const result = groupBy(arr, 'group', 'question.templateId');

console.log(result);