Pluck Unique Values from Array of Javascript Objects

pluck-unique-values-from-array-of-javascript-objects.md

Pluck Unique Values from Array of Javascript Objects

Implementation

const pluck = key => array => Array.from(new Set(array.map(obj => obj[key])));

Usage

const cars = [
  { brand: 'Audi', color: 'black' },
  { brand: 'Audi', color: 'white' },
  { brand: 'Ferarri', color: 'red' },
  { brand: 'Ford', color: 'white' },
  { brand: 'Peugot', color: 'white' }
];

const getBrands = pluck('brand');

console.log(getBrands(cars));

Output

[
  "Audi",
  "Ferarri",
  "Ford",
  "Peugot"
]

very useful

How bout nested properties? Say i want to want to count colours. I should pluck the nested prop (colors.color == 'Black') then check for length. How do i do this?

const cars = [
  {
    "brand": "Audi",
    "model": "A1",
    "colors": [
      {
        "color": "Black"
      },
      {
        "color": "Blue"
      }
    ]
  },
  {
    "brand": "Ferrari",
    "model": "Spyder",
    "colors": [
      {
        "color": "Black"
      },
      {
        "color": "Red"
      }
    ]
  },
  {
    "brand": "Ford",
    "model": "Ranger",
    "colors": [
      {
        "color": "Blue"
      },
      {
        "color": "Grey"
      }
    ]
  },
  {
    "brand": "Peugeot",
    "model": "208 GTi",
    "colors": [
      {
        "color": "Blue"
      },
      {
        "color": "Grey"
      }
    ]
  }
]

A pluck function does not do inner loops so it isn't a good fit for that @rognales. You could get nested properties with a modified pluck that takes a path like pluck('child.grandChild.greatGrandChild') for example, but your data has an Array of colors where you want to do an inner loop to get all of them. If you wanted to only get the first color from each Car for example, pluck would be relevant there because you could do pluck('colors.0') which would return [{ color: "Black" }, { color: "Black" }, { color: "Blue" }, { color: "Blue" }] but that's not what you want.

Maybe something bespoke like this would be better for that situation:

const colorSumsByName = {};

cars.forEach((car) => {
  car.colors.forEach(({ color: colorName }) => {
    colorSumsByName[colorName] = colorSumsByName[colorName] || 0;
    colorSumsByName[colorName] += 1;
  });
});

console.log(colorSumsByName);

Output

{ Black: 2, Blue: 3, Red: 1, Grey: 2 }