Error encountered when utilizing lodash to generate a distinct array from a collection of objects

When using lodash v4.17.10, I encountered the error: 

'LoDashExplicitWrapper<string[]>' is not assignable to type 'string[]'. Property 'length' is missing in type 'LoDashExplicitWrapper<string[]>.'
.

In my scenario, I have an array of objects and I am attempting to extract an array containing only the unique values of a specific property from each object.

The following code snippet illustrates my approach:

let carMakes: string[]
const inventory = [
  { make: "ford", model: "Focus" },
  { make: "ford", model: "F-150" },
  { make: "chevy", model: "Camaro" }

carMakes = _.chain(inventory)
            .map('make')
            .uniq()

I am curious if there is a way to achieve this desired functionality using method chaining in lodash. While it appears to provide an elegant solution, I have been unsuccessful in implementing it within my Angular project.

arraystypescriptuniquelodash

Answer №1

To easily achieve the desired outcome, utilize a basic js Set and apply the map() function once. Then, convert it back to an array using Array.from() to obtain the necessary string[]. 

const catalog = [{
    brand: "apple",
    product: "iPhone"
  },
  {
    brand: "samsung",
    product: "Galaxy"
  },
  {
    brand: "google",
    product: "Pixel"
  }
];

const uniqueBrands = Array.from(new Set(catalog.map(({brand}) => brand)));
console.log(uniqueBrands);

Answer №2

It's amazing how obvious it seems now. Checking out the documentation for lodash regarding the _.chain() method reveals:

By creating a special lodash wrapper instance with method chain sequences enabled, you can wrap a value and perform operations on it. To get the final result, remember to use _#value.

So, all that was missing was:

carMakes = _.chain(inventory)
            .map('make')
            .uniq()
            .value()

I had attempted this approach previously, but strangely enough, the error indication in VS Code persisted until I hovered over value(), after which the error disappeared. Since I hadn't done that before, I assumed it wasn't working.

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