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Functional Programming Patterns With RamdaJS!

Bang for Your Buck: Solution Review

Solution review.

We'll cover the following...

Review

Let’s review the steps

  1. Get everything maxPrice or less
  2. Sort by rating
  3. Get the top 3

Here’s a vanilla solution

Javascript (babel-node)
import menu from './menu';
const getTop3MealsFor = (maxPrice, menu) => menu
    .filter((item) => item.price <= maxPrice)
    .sort((a, b) => b.rating - a.rating)
    .slice(0, 3);
const result = getTop3MealsFor(12, menu);
console.log({ result });

Ramda has slice and sort functions. Using them lets us pipe the entire function to make it point-free.

Javascript (babel-node)
import { pipe, slice, sort } from 'ramda';
import menu from './menu';
const getTop3MealsFor = pipe(
  (maxPrice, menu) => menu.filter((item) => item.price <= maxPrice),
  sort((a, b) => b.rating - a.rating),
  slice(0, 3)
);
const result = getTop3MealsFor(12, menu);
console.log({ result });

We can point-free up filter's predicate function using propSatisfies. It tests an object’s property against a function to return true or false.

Javascript (babel-node)
import { gte, pipe, propSatisfies, slice, sort } from 'ramda';
import menu from './menu';
const getTop3MealsFor = pipe(
  (maxPrice, menu) => menu.filter(propSatisfies(gte(maxPrice), 'price')),
  sort((a, b) => b.rating - a.rating),
  slice(0, 3)
);
const result = getTop3MealsFor(12, menu);
console.log({ result });

I personally wouldn’t do that, but it’s fun to experiment.

Comparators

I would, however, play around with comparators. These are functions that compare data for sorting.

Ramda’s descend function is a descending comparator, meaning a function that sorts entries from biggest to smallest. The flip side would be R.ascend, an ascending comparator.

We can break the sorting logic into a function

const byPrice = descend(prop('rating'));

Then use it like so

sort(byPrice);

It reads like a sentence!

Javascript (babel-node)
import { descend, gte, pipe, prop, propSatisfies, slice, sort } from 'ramda';
import menu from './menu';
const byPrice = descend(prop('rating'));
const getTop3MealsFor = pipe(
  (maxPrice, menu) => menu.filter(propSatisfies(gte(maxPrice), 'price')),
  sort(byPrice),
  slice(0, 3)
);
const result = getTop3MealsFor(12, menu);
console.log({ result });