Find minimum value and a target property in an array of objects

Question

I have an array like this:

var data = [
  { id: 537, name: "aBase" },
  { id: 1, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 8 } },
  { id: 2, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 10 } },
  { id: 3, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 5 } },
  { id: 4, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 2 } },
];

and I want the id of the 'aBase' object and the min y of all of the 'aCourt' objects. The output I want should be something like this:

result = [{id:537,y:2}]

My code so far is like this

let result = [];
data.map((item) => {
    if (item.name === "aBase") {
      if (!result[item.id] === item.id) {
        result[item.id] = item.id;
      }
    } else {
      if (item.name === "aCourt") {
        if (result[item.id] === item.aBaseId) {
          if (!result[item.id].y || result[item.id].y > item.rating.y) {
            result[item.id].y = item.rating.y;
          }
        }
      }
    }
});

How can I fix the code to produce the desired output?

both of the things can be separately calculated using forEach , dont complicate it with using other functions like map — ashish singh
– ashish singh, Commented May 22, 2020 at 20:46
Will the aBase element always be first in data? If so, you can just use result = [{ id: data[0]['id'], y: Math.min(...data.slice(1).map(e => e.rating.y)) }] — applemonkey496
– applemonkey496, Commented May 22, 2020 at 21:09

ggorlen · Accepted Answer · 2020-05-22 21:17:01Z

Array#reduce can do it with a condition to find your base and Math.min to find the lowest e.rating.y:

const data = [
  { id: 537, name: "aBase" },
  { id: 1, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 8 } },
  { id: 2, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 10 } },
  { id: 3, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 5 } },
  { id: 4, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 2 } },
];

const res = data.reduce((a, e) => {
  if (e.name === "aBase") {
    a.id = e.id;
  }
  else {
    a.y = Math.min(a.y, e.rating.y);
  }
  
  return a;
}, {y: Infinity});

console.log(res);

Your expected output wraps this in a single-element array, but this seems unnecessary, so I've omitted it.

Another alternative is using find to collect the base, then map everything else to its y rating, then take the min. The downside is two passes.

const data = [
  { id: 537, name: "aBase" },
  { id: 1, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 8 } },
  { id: 2, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 10 } },
  { id: 3, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 5 } },
  { id: 4, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 2 } },
];

const res = {
  id: data.find(e => e.name === "aBase").id,
  y: Math.min(...data.map(({rating}) => rating ? rating.y : Infinity))
};

console.log(res);

As pointed out in the comments, if you can guarantee aBase as the first element, then you can simplify the above code a bit:

const data = [
  { id: 537, name: "aBase" },
  { id: 1, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 8 } },
  { id: 2, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 10 } },
  { id: 3, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 5 } },
  { id: 4, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 2 } },
];

const res = {
  id: data[0].id,
  y: Math.min(...data.slice(1).map(({rating}) => rating.y))
};

console.log(res);

Carsten Massmann · Accepted Answer · 2020-05-22 22:12:30Z

The following should also work for an arbitrary number of elements in your array. It will combine the data of elements with the same id and aBaseIds into a common result object. The order of elements is immaterial.

var data = [
  { id: 123, name: "aBase"},
  { id: 537, name: "aBase" },
  { id: 1, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 8 } },
  { id: 2, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 10 } },
  { id: 3, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 5 } },
  { id: 4, name: "aCourt", aBaseId: 537, rating: { x: 6.4, y: 2 } },
  { id: 5, name: "aCourt", aBaseId: 123, rating: { x: 6.4, y: 17 } },
  { id: 6, name: "aCourt", aBaseId: 123, rating: { x: 6.4, y: 12 } }
];
var res=data.filter(c=>c.name=='aBase')
 .map(c=>({id:c.id, y: Math.min.apply(null,data.filter(e=>e.aBaseId==c.id).map(f=>f.rating.y))}));
console.log(res);

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