Questions (and solutions) for functional programming

functional-programming-questions.js

/*
	1) Write a function sum() and a function multiply() that sums and multiplies (respectively)
	   all the numbers in an array of numbers. For example, sum([1,2,3,4]) should return 10,
	   and multiply([1,2,3,4]) should return 24.
*/

/*
	2) Write a function max() that takes an array of numbers and returns the largest of them.
*/


/*
	3) Write a function findLongestWord() that takes an array of words and returns the length of the longest one.
*/

/*
	4) Write a function onlyStrings() that takes an array of different types of values,
	   and returns an array of strings only.
 */

/*
	5) Write a function oneEven() that returns true if at least one of the numbers in an array is even.
*/

/*
	6) Write a function even() that returns true if and only if all the numbers in an array are even.
*/

/*
	7) Write a function alolexox() that doubles every consonant and place an occurrence of "o" in between.
	   For example, translate("this is fun") should return the string "tothohisos isos fofunon"
*/

/*
	8) Write a function kraken() that accepts an array, removes everything is not a string,
	   and returns the concatenation of all of the strings, preceded by 'DD - '
	   e.g. [1, false, [1, 2], 'a', 'b', {a: 1}, 'c'] // DD - abc
*/

functional-programming-solutions.js

/*
	1) Write a function sum() and a function multiply() that sums and multiplies (respectively)
	   all the numbers in an array of numbers. For example, sum([1,2,3,4]) should return 10,
	   and multiply([1,2,3,4]) should return 24.
*/

// 1.a
let sum = numbers => numbers.reduce((prev, curr) => prev + curr);

// 1.b
let multiply = numbers => numbers.reduce((prev, curr) => prev * curr);

/*
	2) Write a function max() that takes an array of numbers and returns the largest of them.
*/

function max(numbers) {
	return numbers.reduce((prev, curr) => Math.max(prev, curr));
};

let max = numbers => Math.max(...numbers);

/*
	3) Write a function findLongestWord() that takes an array of words and returns the length of the longest one.
*/

let findLongestWord = words => words.reduce((prev, curr) => prev.length > curr.length ? prev : curr).length;

/*
	4) Write a function onlyStrings() that takes an array of different types of values, and returns an array of strings only.
 */

let onlyStrings = items => items.filter(item => typeof item === 'string');

/*
	5) Write a function oneEven() that returns true if at least one of the numbers in an array is even.
*/

let oneEven = numbers => numbers.some(number => number % 2 === 0);

/*
	6) Write a function even() that returns true if and only if all the numbers in an array are even.
*/

let even = numbers => numbers.every(number => number % 2 === 0);

/*
	7) Write a function alolexox() that doubles every consonant and place an occurrence of "o" in between.
	   For example, translate("this is fun") should return the string "tothohisos isos fofunon"
*/

let alolexox = (phrase) => {
	let escapes = ['a', 'e', 'i', 'o', 'u', ' '];

	return phrase
		.split('')
		.map(letter => escapes.indexOf(letter) === -1 ? letter + 'o' + letter : letter)
		.join('');
}

/*
	8) Write a function kraken() that accepts an array, removes everything is not a string,
	   and returns the concatenation of all of the strings, preceded by 'DD - '
	   e.g. [1, false, [1, 2], 'a', 'b', {a: 1}, 'c'] // DD - abc
*/

let kraken = stuff => stuff.filter(item => typeof item === 'string').reduce((master, piece) => master + piece, 'DD - ');