Analysing an array of objects data using my function and Math.max

Question

Assuming an array of objects that has a couple hundred fields that look like this

[
  {
    "designation":"419880 (2011 AH37)",
    "discovery_date":"2011-01-07T00:00:00.000",
    "h_mag":19.7,
    "moid_au":0.035,
    "q_au_1":0.84,
    "q_au_2":4.26,
    "period_yr":4.06,
    "i_deg":9.65,
    "pha":true,
    "orbit_class":"Apollo"
  }

I'm trying to show the maximum "h_mag" value for all of the data points that I have isolated with the following function:

function filterByPHA (neowise){
  for (let i = 0; i < neowise.length; i++) {
    let neo = neowise[i];
    if (neo.pha === true) {
      console.log(`${neo.designation}: ${neo.orbit_class}`);
    }
  }
}
filterByPHA(neowise);

The function works.

I have tried the following:

const maxMOID = Math.max(...filterByPHA(neowise).map(function(x){
  return x.moid_au;
}));

console.log(maxMOID);

What I think this code should be doing is 'applying' Math.max to my function ('filterByPHA(neowise)' and 'mapping' it onto a new function that returns the maximum moid value for the array inside 'filterByPHA(neowise)'. However, the .map is giving me a 'TypeError: Cannot read properties of undefined (reading 'map')'. The 'x' is just a placeholder. I'm not actually clear on what I need to be putting there to make this code work, or if even it could be a functional bit of code.

Answer 1

You can use Math.max function along with spread syntax to achieve this.

Refer to the following code :

function filterByPHA(neowise) {
  let filteredPHA = neowise.filter(neo => neo.pha === true);

  if (filteredPHA.length > 0) {
    let maxHMAG = Math.max(...filteredPHA.map(neo => neo.h_mag));
    console.log(`Maximum h_mag for PHA objects: ${maxHMAG}`);
  } else {
    console.log("No PHA objects found");
  }
}

const neowiseData = [
  {
    "designation": "419880 (2011 AH37)",
    "discovery_date": "2011-01-07T00:00:00.000",
    "h_mag": 19.7,
    "moid_au": 0.035,
    "q_au_1": 0.84,
    "q_au_2": 4.26,
    "period_yr": 4.06,
    "i_deg": 9.65,
    "pha": true,
    "orbit_class": "Apollo"
  },
  {
    "designation": "419880 (2011 AH38)",
    "discovery_date": "2011-01-07T00:00:00.000",
    "h_mag": 20.7,
    "moid_au": 0.035,
    "q_au_1": 0.84,
    "q_au_2": 4.26,
    "period_yr": 4.06,
    "i_deg": 9.65,
    "pha": true,
    "orbit_class": "Apollo"
  }
];

console.log(filterByPHA(neowiseData));