## Javascript array calculation and transformation

javascript map

javascript array methods

javascript multidimensional array

javascript array reduce

javascript array contains

javascript array foreach

javascript map array of objects

I currently struggle to program a receipt calculator. I want to `map`

over an array with a specific value, then round the numbers and convert they to a string with commas instead of dots.

let ingredients = [0.02, 0.05, 0.5, 1.2]; let map = ingredients.map(x => x * 6); for (let entry of map) { entry.toFixed(2).replace(".", ","); console.log(entry); }

One solution to the precision problem you are facing when performing arithmetic operations with float numbers could be approached using a **correction factor**. A `correction factor`

will be that number you need to multiply to the float number so that it gets converted into an integer. In this sense, all the arithmetic operations will now perform between integers numbers. You can check the next code to see how to use a `correction factor`

in this particular case:

let quantity = 6; let ingredients = [0.02, 0.05, 0.5, 1.2]; // Define a correction factor for arithmetic operations within // the set of float numbers available on ingredients. let cf = Math.pow(10, 2); let map = ingredients.map(x => { let res = (x * cf) * (quantity * cf) / (cf * cf); return res.toString().replace(".", ","); }); let mapRounded = ingredients.map(x => { let res = (x * cf) * (quantity * cf) / (cf * cf); return Math.ceil(res); }); console.log("Original: ", map, "Rounded-Up: ", mapRounded);

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**JavaScript Array map() Method: Transforming Array Elements,** Sometimes, you need to take an array, transform its elements, and include the how to calculate the area of each circle and push the result into a new array. Incoming Array members are of type T, and the output Array contains members of type U. That is to say, we’re free to transform the members of this Array into a completely different data type. The crux of map is that each member of the outbound Array should correspond 1:1 with a member of the inbound Array.

`entry.toFixed(2).replace(".", ",")`

doesn't change the `entry`

it `return`

a new value.**You need to assign entry a new value.**

let quantity = 4; let ingridients = [ 0.02, 0.05, 0.5, 1.2 ]; let map = ingridients.map(x => x * quantity); for (let entry of map) { entry = entry.toFixed(2).replace(".", ","); console.log(entry); }

**Array methods,** an array. Let's move on to methods that transform and reorder an array. They are used to calculate a single value based on the array. Arrays are a special type of objects. The typeof operator in JavaScript returns "object" for arrays. But, JavaScript arrays are best described as arrays. Arrays use numbers to access its "elements". In this example, person[0] returns John:

`entry.toFixed(2).replace(".", ",");`

doesn't change `entry`

. You need to assign it to something.

let formatted = entry.toFixed(2).replace(".", ",") console.log( formatted )

**JavaScript Map, Reduce, and Filter,** Each one will iterate over an array and perform a transformation or computation. Each will return a new array based on the result of the function. You will now figure out if it's a "string" or an Array "object". If it's a string, you can use the JSON.parse method as @alcuadrado suggest, otherwise you can simply use the array. Several answers suggest the use of the for-in statement to iterate over the array elements, I would discourage you to use it for that.

Both `.toFixed`

and `replace`

are *pure* (as any other method working with primitives) that means they do not change the referenced value itself but return a new value. If you'd do

console.log(entry.toFixed(2).replace(".", ","));

you would log the wanted returned value.

**Matrix math for the web,** Matrices can be used to represent transformations of objects in space, and key types of computation when constructing images and visualizing data on the Web. In JavaScript, it is easy to represent a matrix as an array. The JavaScript method toString () converts an array to a string of (comma separated) array values.

let ingridients = [ 0.02, 0.05, 0.5, 1.2 ]; let quantity = 6; let map = ingridients .map(x => x * quantity) .map(n => n.toFixed(2).replace(".", ",")); for (let entry of map) { console.log(entry); }

**Array.from(),** The Array.from() static method creates a new, shallow-copied Array instance from an array-like or iterable object. JavaScript Demo: Array.from(). xxxxxxxxxx. 1 The definition of 'Array.from' in that specification. ECMAScript� In JavaScript, it is easy to represent a matrix as an array. Let's begin by considering the identity matrix. This is a special transformation matrix which functions much like the number 1 does in scalar multiplication; just like n * 1 = n, multiplying any matrix by the identity matrix gives a resulting matrix whose values match the original matrix.

**Chapter 18. Arrays,** Such a literal enumerates the array elements; an element's position implicitly specifies key P (a string!) must be equal to the result of the following computation: of an array; transformation methods derive a new array from the receiver; and� See the Pen javascript-math-exercise-18 by w3resource (@w3resource) on CodePen. Improve this sample solution and post your code through Disqus. Previous: Write a JavaScript function to calculate the sum of values in an array. Next: Create a Pythagorean function in JavaScript

**Functional JavaScript: How to use array reduce for more than just ,** The array reduce method is really powerful. Convert an array to an object;; Unfold to a larger array;; Make two calculations in one traversal;; Combine So, we can use .reduce() to transform short arrays into longer ones. The call to new Array(number) creates an array with the given length, but without elements. The length property is the array length or, to be precise, its last numeric index plus one. It is auto-adjusted by array methods. If we shorten length manually, the array is truncated. We can use an array as a deque with the following operations:

**Arrays and matrices,** Matrices can be created, manipulated, and used in calculations. A Matrix is an object wrapped around a regular JavaScript Array , providing utility index, matrix) { console.log('value:', value, 'index:', index) }) // Apply a transformation on the� Operator precedence in JavaScript is the same as is taught in math classes in school — Multiply and divide are always done first, then add and subtract (the calculation is always evaluated from left to right).

##### Comments

- On a side note, it's written
`ingredients`

, not`ingridients`

. - Thanks. This was the must useful answer to my problem. Im now trying to implement that if map[2] has a comma (eg. 3,5) it should always round up to the next integer... like 4. Can you help me with that?
- @aura199x you can create another map of rounded-up elements, with
`Math.ceil()`

. I have updated my answer, check if this helps you. - Is this the more elegant way? Or the answer from @Maheer Ali ? Thanks