Compare JavaScript Array of Objects to Get Min / M

Question

I have an array of objects and I want to compare those objects on a specific object property. Here's my array:

var myArray = [
    {"ID": 1, "Cost": 200},
    {"ID": 2, "Cost": 1000},
    {"ID": 3, "Cost": 50},
    {"ID": 4, "Cost": 500}
]

I'd like to zero in on the "cost" specifically and a get a min and maximum value. I realize I can just grab the cost values and push them off into a javascript array and then run the Fast JavaScript Max/Min.

However is there an easier way to do this by bypassing the array step in the middle and going off the objects properties (in this case "Cost") directly?

Answer 1

Try (a is array, f is field to compare)

let max= (a,f)=> a.reduce((m,x)=> m[f]>x[f] ? m:x);
let min= (a,f)=> a.reduce((m,x)=> m[f]<x[f] ? m:x);

let max= (a,f)=> a.reduce((m,x)=> m[f]>x[f] ? m:x);
let min= (a,f)=> a.reduce((m,x)=> m[f]<x[f] ? m:x);

// TEST

var myArray = [
    {"ID": 1, "Cost": 200},
    {"ID": 2, "Cost": 1000},
    {"ID": 3, "Cost": 50},
    {"ID": 4, "Cost": 500}
]

console.log('Max Cost', max(myArray, 'Cost'));
console.log('Min Cost', min(myArray, 'Cost'));

console.log('Max ID', max(myArray, 'ID'));
console.log('Min ID', min(myArray, 'ID'));

Answer 2

Adding onto Tristan Reid's answer (+ using es6), you could create a function that accepts a callback, which will contain the operator you want to be applied to the prev and curr:

const compare = (arr, key, callback) => arr.reduce((prev, curr) =>
    (callback(prev[key], curr[key]) ? prev : curr), {})[key];

    // remove `[key]` to return the whole object

Then you could simply call it using:

const costMin = compare(myArray, 'Cost', (a, b) => a < b);
const costMax = compare(myArray, 'Cost', (a, b) => a > b);