Algorithm Optimisation in Node, Javascript

Question

Given the following json array

const groups=[{ id:1, parent:null, groupName:'Others', maxScore:3}, {id:2, parent:null, groupName: 'Group 1', maxScore:0}, {id:3, parent:2, groupName:'Others, maxScore:2}, {id:4, parent:2, groupName:'Sub Group 1', maxScore:1}];

What would be a more performance oriented approach to sum maxScores within parents ? It looks like a tree structure, but nodes don't have references to their children.

Im trying a map.reduce approach right now

function addMaxScoreToGroups(groups) {
    return groups.map((group) => {
      const newGroup = group;
      if (group.parent === null && group.name !== 'Others') {
        const children = groups.filter(elem => elem.parent === group.id);
          if (children) {
            newGroup.maxScore = children.map(x => x.maxScore)
           .reduce((value, acum) => value + acum);
          }
      }
      return newGroup;
    });
}

Expected result would be

const groups=[{ id:1, parent:null, groupName:'Others', maxScore:3}, {id:2, parent:null, groupName: 'Group 1', maxScore:0,maxPosibleScore:3}, {id:3, parent:2, groupName:'Others, maxScore:2}, {id:4, parent:2, groupName:'Sub Group 1', maxScore:1}];

Questions asking for The Best.... are highly subjective. What performs best for one might not for another. You can use jsPerf or similar sites/tools to test performance on approaches/solution that work/give the correct results and use what fits your scenario best. - If you don't have a working solution yet, then re-phrase the question to focus on that instead. — Nope
– Nope, Commented Apr 25, 2018 at 10:35
It is working actually, but I think it can be optimized in terms of how many times i need to map.reduce to get the correct result. — user2821789
– user2821789, Commented Apr 25, 2018 at 11:45
If your code is working and you are looking for optimization codereview.stackexchange.com might get you better answers as those type of questions are usually off topic on Stackoverflow. See What Questions Are On-Topic and which ones Are not On-Topic — Nope
– Nope, Commented Apr 25, 2018 at 15:23

Ori Drori · Accepted Answer · 2018-04-26 00:53:56Z

1

Iterate the with Array.reduce(). For each object create a new entry (or update existing one in case of parent) by cloning the object using object spread (or Object.assign().

If the object has a parent, create the parent if it doesn't exist, and add/update the maxPossibleScore.

Convert back to array using Object.values().

const groups=[{ id:1, parent:null, groupName:'Others', maxScore:3}, {id:3, parent:2, groupName:'Others', maxScore:2}, {id:4, parent:2, groupName:'Sub Group 1', maxScore:1}, {id:2, parent:null, groupName: 'Group 1', maxScore:5}];
    
const ms = 'maxScore';
const mps = 'maxPossibleScore';
const result = Object.values(groups.reduce((r, o) => {
  // clone
  const c = { ...o };
  
  // if current parent initalized before, update maxPossibleScore
  if(!o.parent && r[o.id]) c[mps] = r[o.id][mps] + c[ms];
  
  r[o.id] = c;
  
  if(o.parent) {
    // if parent doesn't exist init
    r[o.parent] = r[o.parent] || {};
    // if parent.maxPossibleScore doesn't exist init it
    if(!(mps in r[o.parent])) {
      r[o.parent][mps] = r[o.parent][ms] || 0;
    }
    
    r[o.parent][mps] += o[ms];
  }
  
  return r;
}, {}));

console.log(result);

edited Apr 26, 2018 at 0:53

answered Apr 25, 2018 at 10:37

Ori Drori

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5 Comments

Ori Drori Over a year ago

Probably @nope :)

Nope Over a year ago

Why? OP did ask for better performing code, why would your perform better than OPs existing code and how are you determining that? jsPerf or similar?

Ori Drori Over a year ago

Big O notation - O(n) vs. at least O(n^2) (current solution). Since we're I'm using reduce, which invokes callback functions, it's less performant than a simple for loop.

user2821789 Over a year ago

@OriDrori, its not wokring :( If I just have one parent=null, its maxPosibleScore stays 0

Ori Drori Over a year ago

Should be fixed now. If not, add a test case in the comments.

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