✨ Add exercise 7 on collection manipulation (#98)
* ✨ Add exercise 7 on collection manipulation * 💬 Fix hint * 💬 Improve hint
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Hugo Saracino
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89
src/exo7/exo7.test.ts
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89
src/exo7/exo7.test.ts
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import {
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allPageViews,
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intersectionPageViews,
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mapWithConcatenatedEntries,
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mapWithLastEntry,
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nonPrimeOdds,
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numberArray,
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numberArrayFromSet,
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numberSet,
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primeOdds,
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} from './exo7';
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describe('exo7', () => {
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describe('numberSet', () => {
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it('should be the set of unique values from `numberArray`', () => {
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expect(numberSet).toStrictEqual(new Set(numberArray));
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});
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});
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describe('numberArrayFromSet', () => {
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it('should be the array of unique values from `numberArray`', () => {
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expect(numberArrayFromSet).toStrictEqual(
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[...new Set(numberArray)].sort((a, b) => a - b),
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);
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});
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});
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describe('mapWithLastEntry', () => {
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it('should construct the map from `associativeArray` keeping only the last entry for colliding keys', () => {
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expect(mapWithLastEntry).toStrictEqual(
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new Map([
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[1, 'Alice'],
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[3, 'Clara'],
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[4, 'Denise'],
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[2, 'Robert'],
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]),
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);
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});
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});
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describe('mapWithConcatenatedEntries', () => {
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it('should construct the map from `associativeArray` concatenating values for colliding keys', () => {
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expect(mapWithConcatenatedEntries).toStrictEqual(
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new Map([
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[1, 'Alice'],
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[3, 'Clara'],
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[4, 'Denise'],
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[2, 'BobRobert'],
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]),
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);
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});
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});
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describe('nonPrimeOdds', () => {
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it('should contain only the odd numbers that are not prime', () => {
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expect(nonPrimeOdds).toStrictEqual(new Set([1, 9]));
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});
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});
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describe('primeOdds', () => {
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it('should contain only the odd numbers that are also prime', () => {
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expect(primeOdds).toStrictEqual(new Set([3, 5, 7]));
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});
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});
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describe('allPageViews', () => {
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it('should contain the map of aggregated page views from both sources of analytics', () => {
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expect(allPageViews).toStrictEqual(
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new Map([
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['home', { page: 'home', views: 15 }],
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['about', { page: 'about', views: 2 }],
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['blog', { page: 'blog', views: 42 }],
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['faq', { page: 'faq', views: 5 }],
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]),
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);
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});
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});
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describe('intersectionPageViews', () => {
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it('should contain the map of intersecting page views from both sources of analytics', () => {
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expect(intersectionPageViews).toStrictEqual(
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new Map([
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['home', { page: 'home', views: 15 }],
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['blog', { page: 'blog', views: 42 }],
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]),
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);
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});
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});
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});
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187
src/exo7/exo7.ts
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src/exo7/exo7.ts
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// `fp-ts` training Exercise 7
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// Manipulate collections with type-classes
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import { unimplemented } from '../utils';
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// In this exercise, we will learn how to manipulate essential collections
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// such as `Set` and `Map`.
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//
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// These collections have very important properties that make them slightly
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// more complex than the venerable `Array`:
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// - `Set` requires each element to be unique
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// - `Map` associates unique keys to values
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//
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// In fact, it can sometimes be helpful to think of `Set` as a special case
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// of `Map` where `Set<T>` is strictly equivalent to `Map<T, void>`.
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//
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// To manipulate these collections, we need often need to inform `fp-ts` on
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// how to uphold the properties outlined above (eg. how to determine whether
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// two elements or keys have the same value, how to combine values together
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// in case of key collision or how to order the values when converting back
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// to an array).
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//
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// And the way to describe those properties for the specific inner types of a
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// given `Set` or `Map` is... TYPECLASSES!
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///////////////////////////////////////////////////////////////////////////////
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// SET //
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///////////////////////////////////////////////////////////////////////////////
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// A `Set` is pretty straightforward, it stores values but doesn't care at all
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// about the ordering of those values. Furthermore, it ignores duplicates.
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export const numberArray: ReadonlyArray<number> = [7, 42, 1337, 1, 0, 1337, 42];
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// Construct `numberSet` from the provided `numberArray`.
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// You need to use the `ReadonlySet` module from `fp-ts` instead of the
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// JavaScript standard constructor.
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//
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// HINTS:
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// - You can look into `readonlySet.fromReadonlyArray`
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// - `fp-ts` doesn't know how you want to define equality for the inner type
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// and requires you to provide an `Eq` instance
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export const numberSet: ReadonlySet<number> = unimplemented();
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// Convert `numberSet` back to an an array in `numberArrayFromSet`.
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// You need to use the `ReadonlySet` module from `fp-ts` instead of the
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// JavaScript standard constructor.
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//
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// HINTS:
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// - You can look into `readonlySet.toReadonlyArray`
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// - The elements in `numberSet` have no guarantees whatsoever regarding
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// their ordering. This ordering could be totally random. But remember that
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// functional programming is all about purity. Converting a set to an array
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// is a pure operation and as such, should return the same value for the
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// same input. This means you **need** to instruct `fp-ts` on how you wish
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// the values to be ordered in the output array, by providing an `Ord`
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// instance.
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export const numberArrayFromSet: ReadonlyArray<number> = unimplemented();
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///////////////////////////////////////////////////////////////////////////////
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// MAP //
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///////////////////////////////////////////////////////////////////////////////
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// A `Map` associates a set of unique keys to arbitrary values. Values
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// themselves can be duplicated across various keys but keys have to be unique.
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//
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// This means than when constructing a `Map` from an `Array`, you need to be
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// explicit on how you wish to combine values in case of key collision (maybe
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// you want to only insert the last value provided, maybe the first, maybe you
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// want to combine both values in a specific way eg. concatenate strings, add
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// numbers, etc...)
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export const associativeArray: ReadonlyArray<[number, string]> = [
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[1, 'Alice'],
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[2, 'Bob'],
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[3, 'Clara'],
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[4, 'Denise'],
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[2, 'Robert'],
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];
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// Construct `mapWithLastEntry` from the provided `associativeArray`.
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// You need to use the `ReadonlyMap` module from `fp-ts` instead of the
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// JavaScript standard constructor.
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//
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// The resulting `Map` should have the following shape:
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// 1 => 'Alice'
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// 2 => 'Robert'
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// 3 => 'Clara'
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// 4 => 'Denise'
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//
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// HINTS:
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// - You can look into `readonlyMap.fromFoldable`
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// - You need to provide an `Eq` instance for the key type
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// - You need to provide a `Magma` instance for the value type. In this case,
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// the `Magma` instance should ignore the first value and return the second.
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// (You can define your own, or look into the `Magma` or `Semigroup` module)
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// - You need to provide the `Foldable` instance for the input container type.
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// Just know that you can construct a `Map` from other types than `Array` as
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// long as they implement `Foldable`. Here, you can simply pass the standard
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// `readonlyArray.Foldable` instance.
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export const mapWithLastEntry: ReadonlyMap<number, string> = unimplemented();
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// Same thing as above, except that upon key collision we don't want to simply
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// select the newest entry value but append it to the previous one.
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//
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// Basically, the resulting `Map` here should have the following shape:
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// 1 => 'Alice'
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// 2 => 'BobRobert'
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// 3 => 'Clara'
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// 4 => 'Denise'
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//
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// HINT:
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// - You can look into the `Semigroup` typeclass as it is a super-class of
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// `Magma`, meaning that a `Semigroup<A>` is also necessarily a `Magma<A>`.
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// The `string` module may contain what you need ;)
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//
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// Bonus point:
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// Did you find something helpful in the `Semigroup` module that may have been
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// helpful in defining `mapWithLastEntry`?
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export const mapWithConcatenatedEntries: ReadonlyMap<number, string> =
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unimplemented();
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///////////////////////////////////////////////////////////////////////////////
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// DIFFERENCE / UNION / INTERSECTION //
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///////////////////////////////////////////////////////////////////////////////
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export const primes = new Set([2, 3, 5, 7]);
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export const odds = new Set([1, 3, 5, 7, 9]);
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// Construct the set `nonPrimeOdds` from the two sets defined above. It should
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// only include the odd numbers that are not prime.
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//
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// HINT:
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// - Be mindful of the order of operands for the operator you will chose.
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export const nonPrimeOdds: ReadonlySet<number> = unimplemented();
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// Construct the set `primeOdds` from the two sets defined above. It should
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// only include the odd numbers that are also prime.
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export const primeOdds: ReadonlySet<number> = unimplemented();
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///////////////////////////////////////////////////////////////////////////////
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export type Analytics = {
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page: string;
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views: number;
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};
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// These example maps are voluntarily written in a non fp-ts way to not give
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// away too much obviously ;)
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//
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// As an exercise for the reader, they may rewrite those with what they've
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// learned earlier.
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export const pageViewsA = new Map(
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[
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{ page: 'home', views: 5 },
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{ page: 'about', views: 2 },
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{ page: 'blog', views: 7 },
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].map(entry => [entry.page, entry]),
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);
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export const pageViewsB = new Map(
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[
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{ page: 'home', views: 10 },
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{ page: 'blog', views: 35 },
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{ page: 'faq', views: 5 },
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].map(entry => [entry.page, entry]),
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);
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// Construct the map with the total page views for all the pages in both sources
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// of analytics `pageViewsA` and `pageViewsB`.
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//
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// In case a page appears in both sources, their view count should be summed.
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export const allPageViews: ReadonlyMap<string, Analytics> = unimplemented();
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// Construct the map with the total page views but only for the pages that
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// appear in both sources of analytics `pageViewsA` and `pageViewsB`.
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export const intersectionPageViews: ReadonlyMap<string, Analytics> =
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unimplemented();
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1
src/exo7/index.ts
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1
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export * from './exo7';
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