#reduceright

[undeadgoathead]

Thanks to @reducerightmusic for the sick T shirt! Rock on! 😎🤘🏼 . #reduceright #rock #rockmusic #rocknroll #rocker #rockerchick #rockstyle #rockstar #metal #metalhead #headbanger #metalblogger #metalchick #mosher #thrasher #hesher #undead #goathead #music #musicblog #heavymetal #punkrock #punk #punkgirl #grunge #grungeaesthetic #grungegirl #alternative #lifestyle https://www.instagram.com/p/CiG-nnAOa9n/?igshid=NGJjMDIxMWI=

[phungthaihy]

JavaScript Array Methods , flat , flatMap , reduceRight, copyWithin http://ehelpdesk.tk/wp-content/uploads/2020/02/logo-header.png [ad_1] New JavaScript Prototype Array M... #androiddevelopment #angular #arraymethods #c #copywithin #css #dataanalysis #datascience #deeplearning #development #docker #flatmap #iosdevelopment #java #javascript #javascriptarraymethods #machinelearning #node.js #python #react #reduceright #unity #webdevelopment

[pheonixsolutions]

Arrays in Javascript

Arrays in Javascript Date: 19/02/2020

Introduction

Array in Javascript has some of the in-built methods that are very much handy when manipulating the array contents than whatever operation you can do with forEach or for a loop. If you know how to handle those in-built methods, you can tackle some of the complex logic without complex implementations. I do use them in everyday work. In this tutorial, though I will not all of those in-built methods, will explain the most useful methods. Map Array.prototype.map(currentValue, index, array) let 1dArrray = let 2dArray = 1dArray.map((currentValue) => { return }); console.log(2dArray) // , , , ] What happens behind is that no matter what work you do inside the parenthesis it will replace the currentValue with the value you return eventually. If you don't 'undefined' will be there. In other words, the transformation will happen with a current array value. Note: it will array with same size Filter Array.prototype.filter(currentValue, index, array) let oddEven = let even = oddEven.map((currentValue) => { return currentValue % 2 == 0 }); console.log(even) // In this filter case, the difference with a map is it will return array value that satisfies the return statement inside the parenthesis. Note: it may or may not array with the same size depending on what you do. but the returned array will be a new array. Reduce: Array.prototype.reduce((prev, next),initialValue) let ones = let sum = ones.reduce((prev, next) => { return prev + next; }, 100) console.log(sum) // 106 The reduce function is very different from the map or filter. It will one return a Number for your array of numbers. If you didn't mention initial value, it will take the array value at index 0 as the initial value and index at 1 as the next value for the first iteration. If there is no next value, then iteration will stop as know. You can also check out slice, reduceRight, and others too. Note: splice considered an impure function. To know more about what is pure or not check here https://www.freecodecamp.org/news/what-is-a-pure-function-in-javascript-acb887375dfe/ For more interesting concepts in javascript, check the below. https://javascript.info/ Conclusion Thanks for you. If you found it useful share it with others to keep it afloat. Read the full article

[cyberblogin]

The Ultimate JavaScript Cheat Sheet JavaScript Arrays concat() Join several arrays into one copyWithin() Copy array elements within the array, to and from specified positions indexOf() Return the primitive value of the specified object includes() Check if an array contains the specified element join() Combine elements of an array into a single string and return the string entries() Return a key/value pair Array Iteration Object every() Check if every element in an array passes a test fill() Fill the elements in an array with a static value filter() Create a new array with every element in an array that pass a test find() Return the value of the first element in an array that pass a test forEach() Call a function for each array element from() Create an array from an object lastIndexOf() Give the last position at which a given element appears in an array pop() Remove the last element of an array push() Add a new element at the end reverse() Sort elements in descending order reduce() Reduce the values of an array to a single value (going left-to-right) reduceRight() Reduce the values of an array to a single value (going right-to-left) shift() Remove the first element of an array slice() Pull a copy of a portion of an array into a new array object sort() Sort elements alphabetically splice() Add elements in a specified way and position unshift() Add a new element to the beginning …

[holytheoristtastemaker]

  We are using arrays all the time every day when coding, probably the most used data structure. Who is working with Javascript is probably relying on many of its powerful array methods such as .map, .filter, .find, .some, .every, .reduce and others. The thing is, array prototype in JS has many other very useful methods and some of them nearly unknown by most of the developers, so let's get into it:

copyWithin(target, start?, end?)

🙇🏻‍♂️ Heads up with this one, it's going to modify the original array and not return a new one

This method will copy elements from the target position to the start position until the end, sounds a little confusing eh?! Let's see some code then

let array = [1,2,3,4,5]; console.log(array.copyWithin(3, 1, 3)) // [1, 2, 3, 2, 3]

So what the heck happened here? Take the elements starting from index 1 untill index 3 and place them starting from the index 3. So let's see another example:

let array = [1,2,3,4,5,6,7,8,9,10]; console.log(array.copyWithin(0,5)) // [6, 7, 8, 9, 10, 6, 7, 8, 9, 10]

So here we are taking the elements starting from 5 until the end of the array and placing them starting from 0. So, in other words, we can understand it like:

array.copyWithin(Where the elements must go, where should it start copying from, where should stop to copy);

Let's see one more trick with it:

let array = [1, 2, 3, 4, 5]; array.copyWithin(2); // [1, 2, 1, 2, 3] // If the target is negative it will copy starting from reverse array = [1, 2, 3, 4, 5]; array.copyWithin(-2); // [1, 2, 3, 1, 2]

lastIndexOf(searchedElement, toIndex?)

This one is particularly very useful, let's see a simple example first:

const fruits = [ 'apple', 'banana', 'strawberry', 'blueberry', 'orange', 'blueberry', 'pineapple', ]; // It will log the index of the last occurency of 'blueberry' console.log(fruits.lastIndexOf('blueberry')); // 5

At some moment you can want to look for the last occurrence only if it's before some specific index, so let's say for example:

const fruits = [ 'apple', 'banana', 'strawberry', 'blueberry', 'orange', 'blueberry', 'pineapple', ]; // You only wanted the last index of 'blueberry' if it was // between the 3 first elements console.log(fruits.lastIndexOf('blueberry', 2)); // -1

But this method can become more interesting when you have more complex objects and you combine it with other array methods. Let's look into it:

const persons = [ { name: 'Charles', age: 26 }, { name: 'Marcos', age: 31 }, { name: 'Jane', age: 22 }, { name: 'Anton', age: 22 }, { name: 'Eduardo', age: 22 }, { name: 'Paula', age: 26 }, ]; // We want to find the index of the last person // who is 22 years old, // unfotunately lastIndexOf doesn't accept a callback // so we gonna transform the array in array of ages that // match the index with the objects and find the last // occurence of 22 persons .map(person => person.age) .lastIndexOf(22); // 4

reduceRight(callBack, initialValue?)

This one is a little funny and very easy to understand, the signature is exactly the same as the original reduce methods and its behavior are quite the same with a small difference: instead iterate from left to right it will do it from right to left ( as the name make it very clear ) so let's jump in some simple example.

const numbers = ["1", "2", "3", "4", "5"]; console.log( numbers.reduce((acc, curr) => { return acc + curr; }, "") ); // "12345" console.log( numbers.reduceRight((acc, curr) => { return acc + curr; }, "") ); // "54321"

This method is very handy when you want to express something from left to right but evaluate it from right to left, let's see a little more complex example:

const add10 = n => n + 10; const divideBy2 = n => n / 2; const commands = [divideBy2, add10]; console.log( commands.reduce((acc, curr) => { return curr(acc); }, 100) ); // 60 console.log( commands.reduceRight((acc, curr) => { return curr(acc); }, 100) ); // 55

I hope something here was new for you and you leave this post knowing at least a little bit more about javascript arrays. Let me know in the comments how do you liked it :)

[etauthenonprogrammercoder]

[GAS][ノンプロ研]与えられた文字列を逆順にする関数

概要

ノンプロ研の今週のお題です。 以前、ボーッとしていたときに文字列を配列操作してしまい、意外と操作できてしまった記憶をもとにコードを書いたよ。

以前ボーッとして書いたコードの概要

var string = 'あいうえお'; Logger.log('string[2]: [%s] %s ', typeof(string[2]), string[2]); // string[2]: [string] う

まとめとコード

デクリメント演算子がどうも苦手というか、頭がごちゃごちゃしてしまうので、インクリメント演算子で書きました。 デクリメント演算子のほうがスッキリすると思うけども、俺はこっちのほうがスッキリします。

function myFunction() { var string = 'hogehoge'; var newString = ''; var length = string.length; for (var i = 0; i < length ; i++) { newString += string[Math.abs(i - length) - 1]; } Logger.log('newString: [%s] %s ', typeof(newString), newString); // newString: [string] egohegoh }

for 文の中は、 string の最終の文字から左に 1 文字ずつを newString に追加してあげてるだけです。 配列操作ができるんなら、配列の reduceRight メソッド使えるんじゃないかなーと思ったけど、こいつはダメだ。

function myFunction2() { var string = ['h', 'o', 'g', 'e', 'h', 'o', 'g', 'e']; // 「var string = 'hogehoge';」では動かない var newString = string.reduceRight(function(previousValue, currentValue) { return previousValue + currentValue; }); Logger.log('newString: [%s] %s ',typeof(newString) , newString); // newString: [string] egohegoh }

string って書いてあるけど、思いっきり array なのはお気になさらず。 string から array への変換は、ボーッとして書いたコードを使って

for (var i = 0; i < string.length; i++) { array[i] = string[i]; } Logger.log('array: [%s] %s ', typeof(array), array); // array: [object] [h, o, g, e, h, o, g, e]

で、書けるよ。外法っぽさむんむんでお送りしました。

[macronimous]

What is the difference between reduce and reduceRight in #JavaScript? https://t.co/XElhFeCaeB https://t.co/rsGJGI6LCI

What is the difference between reduce and reduceRight in #JavaScript? https://t.co/XElhFeCaeB pic.twitter.com/rsGJGI6LCI

— Macronimous.com (@macronimous) November 15, 2018

from Twitter https://twitter.com/macronimous November 15, 2018 at 09:00AM via IFTTT

[t-baba]

10 Lodash Features You Can Replace with ES6

Right now, Lodash is the most depended-on npm package, but if you're using ES6, you might not actually need it.

In this article, we're going to look at using native collection methods with arrow functions and other new ES6 features to help us cut corners around many popular use cases.

1. Map, Filter, Reduce

These collection methods make transforming data a breeze and with near universal support. We can pair them with arrow functions to help us write terse alternatives to the implementations offered by Lodash:

_.map([1, 2, 3], function(n) { return n * 3; }); // [3, 6, 9] _.reduce([1, 2, 3], function(total, n) { return total + n; }, 0); // 6 _.filter([1, 2, 3], function(n) { return n <= 2; }); // [1, 2] // becomes [1, 2, 3].map(n => n * 3); [1, 2, 3].reduce((total, n) => total + n); [1, 2, 3].filter(n => n <= 2);

It doesn't stop here, either. If we're using a modern browser, we can also use find, some, every and reduceRight too.

2. Head & Tail

Destructuring syntax allows us to get the head and tail of a list without utility functions:

_.head([1, 2, 3]); // 1 _.tail([1, 2, 3]); // [2, 3] // becomes const [head, ...tail] = [1, 2, 3];

It's also possible to get the initial elements and the last element in a similar way:

_.initial([1, 2, 3]); // -> [1, 2] _.last([1, 2, 3]); // 3 // becomes const [last, ...initial] = [1, 2, 3].reverse();

If you find it annoying that reverse mutates the data structure, then you can use the spread operator to clone the array before calling reverse:

const xs = [1, 2, 3]; const [last, ...initial] = [...xs].reverse();

3. Rest and Spread

The rest and spread functions allow us to define and invoke functions that accept a variable number of arguments. ES6 introduced dedicated syntaxes for both of these operations:

var say = _.rest(function(what, names) { var last = _.last(names); var initial = _.initial(names); var finalSeparator = (_.size(names) > 1 ? ', & ' : ''); return what + ' ' + initial.join(', ') + finalSeparator + _.last(names); }); say('hello', 'fred', 'barney', 'pebbles'); // "hello fred, barney, & pebbles" // becomes const say = (what, ...names) => { const [last, ...initial] = names.reverse(); const finalSeparator = (names.length > 1 ? ', &' : ''); return `${what} ${initial.join(', ')} ${finalSeparator} ${last}`; }; say('hello', 'fred', 'barney', 'pebbles'); // "hello fred, barney, & pebbles"

4. Curry

Without a higher-level language such as [TypeScript][5] or [Flow][6], we can't give our functions type signatures, which makes currying quite difficult. When we receive curried functions, it's hard to know how many arguments have already been supplied, and which we’ll need to provide next. With arrow functions, we can define curried functions explicitly, making them easier to understand for other programmers:

function add(a, b) { return a + b; } var curriedAdd = _.curry(add); var add2 = curriedAdd(2); add2(1); // 3 // becomes const add = a => b => a + b; const add2 = add(2); add2(1); // 3

These explicitly curried arrow functions are particularly important for debugging:

var lodashAdd = _.curry(function(a, b) { return a + b; }); var add3 = lodashAdd(3); console.log(add3.length) // 0 console.log(add3); // function (a, b) { // /* [wrapped with _.curry & _.partial] */ // return a + b; // } // becomes const es6Add = a => b => a + b; const add3 = es6Add(3); console.log(add3.length); // 1 console.log(add3); // function b => a + b

If we're using a functional library like lodash/fp or ramda, we can also use arrows to remove the need for the auto-curry style:

_.map(_.prop('name'))(people); // becomes people.map(person => person.name);

Continue reading %10 Lodash Features You Can Replace with ES6%

by Dan Prince via SitePoint https://ift.tt/2JWACHw

[macronimous]

What is the difference between #Reduce and reduceRight in #JavaScript? https://t.co/E0uexe2kXq https://t.co/NolEN3qodR

What is the difference between #Reduce and reduceRight in #JavaScript? https://t.co/E0uexe2kXq pic.twitter.com/NolEN3qodR

— Macronimous.com (@macronimous) September 26, 2018

from Twitter https://twitter.com/macronimous September 27, 2018 at 02:25AM via IFTTT