Create a roster of numbers that are multiples using a systematic approach

Question

Create a roster of numbers that are multiples using a systematic approach

Is the following code a functional way to return multiples of 5?

function Mul(start,array,Arr)
{
    Arr[start]=array[start]*5;
 
    if(start>array.length-2){
    return Arr;
    }
   
    return Mul(start+1,array,Arr);
 }    
var numbers =[1,2,3,4,5,6,7,8,9,10];
var Arr=[];

The values are stored in an empty array.

console.log("table ", Mul(0,numbers,Arr));

javascript functional-programming

Answer 1

Answer №1

This code is not entirely functional as it involves mutating the argument passed.

To make it more functional, you can utilize the built-in .map function to transform each element in the array:

const multiplyBy5 = arr => arr.map(item => item * 5);
const modifiedArray = (start, input) => input.slice(0, start).concat(multiplyBy5(input.slice(start)));

console.log("resulting array ", modifiedArray(0, [1,2,3,4,5,6,7,8,9,10]));

(It should be noted that this approach still has a side effect with the console.log)

If you intend to transform the entire array, without the need for the parameter start:

const modifiedArray = arr => arr.map(item => item * 5);

console.log("resulting array ", modifiedArray([1,2,3,4,5,6,7,8,9,10]));

Answer 2

This code is not entirely functional as it involves mutating the argument passed.

To make it more functional, you can utilize the built-in .map function to transform each element in the array:

const multiplyBy5 = arr => arr.map(item => item * 5);
const modifiedArray = (start, input) => input.slice(0, start).concat(multiplyBy5(input.slice(start)));

console.log("resulting array ", modifiedArray(0, [1,2,3,4,5,6,7,8,9,10]));

(It should be noted that this approach still has a side effect with the console.log)

If you intend to transform the entire array, without the need for the parameter start:

const modifiedArray = arr => arr.map(item => item * 5);

console.log("resulting array ", modifiedArray([1,2,3,4,5,6,7,8,9,10]));

Answer 3

Answer №2

Your initial attempt wouldn't be considered functional because it alters the original input.

This presents a problem as, in addition to managing program execution flow, you must also consider data manipulation. For instance:


const last = arr => arr.pop();
const sum = ([a, b]) => a + b;  

const x = [4, 2];
const y = [4, 2];

// Expected Behavior

sum(x);  //=> 6
last(x); //=> 2

// Issue!

last(y); //=> 2
sum(y);  //=> NaN

The problem lies in the fact that Array#pop modifies the array. It becomes apparent that the order of execution now impacts the outcome for the same inputs. This unnecessary complexity leads to program instability and introduces bugs that can be challenging to identify and resolve.

If your goal is to multiply all elements in an array by 5, the most straightforward and functional approach would be using xs.map(x => x * 5).

In functional programming, there's a concept called unfold which generates a list by repeatedly applying a function on a value until a condition is met:

unfold(mult5, 1); // starting with 1 and multiplying by 5 up to 10.
//=> [5, 10, 15, 20, 25, 30, 35, 40, 45, 50]

However, when the boundaries are known beforehand, such as needing the first n multiples of 5, we can optimize the process:

Let's set aside 10 slots for our multiples of five:

const xs = Array(10);
//=> An array of 10 empty values

Note: Mapping over this kind of array won't work!

const ys = xs.map(x => x * 5);
//=> Still an array of 10 empty values!

To address this, use Array.from:

const ys = Array.from(xs, (_, i) => (i + 1) * 5);
//=> [5, 10, 15, 20, 25, 30, 35, 40, 45, 50]

Answer 4

Your initial attempt wouldn't be considered functional because it alters the original input.

This presents a problem as, in addition to managing program execution flow, you must also consider data manipulation. For instance:


const last = arr => arr.pop();
const sum = ([a, b]) => a + b;  

const x = [4, 2];
const y = [4, 2];

// Expected Behavior

sum(x);  //=> 6
last(x); //=> 2

// Issue!

last(y); //=> 2
sum(y);  //=> NaN

The problem lies in the fact that Array#pop modifies the array. It becomes apparent that the order of execution now impacts the outcome for the same inputs. This unnecessary complexity leads to program instability and introduces bugs that can be challenging to identify and resolve.

If your goal is to multiply all elements in an array by 5, the most straightforward and functional approach would be using xs.map(x => x * 5).

In functional programming, there's a concept called unfold which generates a list by repeatedly applying a function on a value until a condition is met:

unfold(mult5, 1); // starting with 1 and multiplying by 5 up to 10.
//=> [5, 10, 15, 20, 25, 30, 35, 40, 45, 50]

However, when the boundaries are known beforehand, such as needing the first n multiples of 5, we can optimize the process:

Let's set aside 10 slots for our multiples of five:

const xs = Array(10);
//=> An array of 10 empty values

Note: Mapping over this kind of array won't work!

const ys = xs.map(x => x * 5);
//=> Still an array of 10 empty values!

To address this, use Array.from:

const ys = Array.from(xs, (_, i) => (i + 1) * 5);
//=> [5, 10, 15, 20, 25, 30, 35, 40, 45, 50]

Answer 5

Answer №3

Don't overlook the power of using recursion in this scenario!

const findFactorial = (num) => {
  if (num <= 1) { return 1; }
  
  return num * findFactorial(num - 1);
};

console.log(
  findFactorial(5),
);

console.log(
  findFactorial(8),
);

Answer 6

Don't overlook the power of using recursion in this scenario!

const findFactorial = (num) => {
  if (num <= 1) { return 1; }
  
  return num * findFactorial(num - 1);
};

console.log(
  findFactorial(5),
);

console.log(
  findFactorial(8),
);

Create a roster of numbers that are multiples using a systematic approach

Answer №1

Answer №2

Answer №3

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