TypeScript vs. C#: LINQ

TypeScript 没有等效于 LINQ 的语言集成自然查询方面?不能在 TypeScript 中写入以下 LINQ 语句

1	`var` `adultUserNames =` `from` `u` `in` `users` `where` `u.Age >= 18` `select` `u.Name;`

但是，位于 LINQ 核心的 iE6<T>扩展方法在 TypeScript 中具有等效项（或可以模拟）。

Aggregate

All

Any

Append

Average

Cast

Concat

Contains

Count

DefaultIfEmpty

Distinct

ElementAt

ElementAtOrDefault

Empty

Except

First

FirstOrDefault

List.ForEach

GroupBy

Intersect

Last

LastOrDefault

Max

Min

OfType

OrderBy / ThenBy

Reverse

select

SelectMany

Single

SingleOrDefault

Skip

SkipWhile

Sum

Take

TakeWhile

Union

where

Zip

Aggregate

// C#

var leftToRight = users.Aggregate(initialValue, (a, u) => /* ... */);

// TypeScript

const leftToRight = users.reduce((a, u) => /* ... */, initialValue);

const rightToLeft = users.reduceRight((a, u) => /* ... */, initialValue);

All

// C#

var allReady = users.All(u => u.IsReady);

// TypeScrip

tconst allReady = users.every(u => u.isReady);

Any

// C#

var isDirty = users.Any(u => u.IsDirty);

// TypeScript

const isDirty = users.some(u => u.isDirty);

Append

// C#

var allUsers = users.Append(oneMoreUser);

// TypeScript

const allUsers = [ ...users, oneMoreUser ];

Average

// C#

var avgAge = users.Average(u => u.Age);

// TypeScript

if (users.length < 1) {

throw new Error(‘source contains no elements‘);

}

const avgAge = users.reduce((a, u) => a + u.age, 0) / users.length;

Cast

// C#

var people = users.Cast<Person>();

// TypeScript

const people = users as Person[];

// Note: not semantically the same. The C# version throws an exception

// if any of the users can‘t be cast to type Person.

//注意：在语义上不同。C# 版本引发异常如果无法强制转换为键入 Person 的任何用户。　

Concat

// C#

var allUsers = users.Concat(moreUsers);

// TypeScript

const allUsers = [ ...users, ...moreUsers ];

Contains

// C#

var hasAdmin = users.Contains(admin);

// TypeScript

const hasAdmin = users.includes(admin); // Use a polyfill for IE support

Count

// C#

var n = users.Count();

// TypeScript

const n = users.length;

DefaultIfEmpty

// C#

var nonEmptyUsers = Enumerable.DefaultIfEmpty(users);

// TypeScript

const nonEmptyUsers = users.length ? users : [ null ];　

Distinct

// C#

var uniqueNames = users.Select(u => u.Name).Distinct();

// TypeScript

const uniqueNames = Object.keys(users.map(u => u.name).reduce((un, u) => ({ ...un, n }),{}));

ElementAt

// C#

var nth = users.ElementAt(n);

// TypeScript

if (n < 0 || n > users.length) {

throw new Error(‘Index was out of range‘);

}

const nth = users[n];　

ElementAtOrDefault

// C#

var nth = users.ElementAtOrDefault(n);

// TypeScript

const nth = users[n];

Empty

// C#

var noUsers = IEnumerable.Empty<User>();//?.NET 4.0 没找到找到的是DefaultIfEmpty

//

var noUsers = IEnumerable.DefaultIfEmpty<User>();

// TypeScript

const noUsers: User[] = [];

const noUsers = [] as User[];

Except

// C#

var maleUsers = users.Except(femaleUsers);

// TypeScript

const maleUsers = users.filter

(

u => !femaleUsers.includes(u) // Use a polyfill for IE support（Use a polyfill for IE support）

);　

First

// C#

var first = users.First();

// TypeScript

if (users.length < 1) {

throw new Error(‘Sequence contains no elements‘);

}

const first = users[0];

FirstOrDefault

// C#

var first = users.FirstOrDefault();

// TypeScript

const first = users[0];

List.ForEach

// C#

users.ToList().ForEach(u => /* ... */);

// TypeScript

users.forEach(u => /* ... */);

GroupBy

// C#

var usersByCountry = users.GroupBy(u => u.Country);

// TypeScript

const usersByCountry = users.reduce((ubc, u) =>

({

...ubc,

[u.country]: [ ...(ubc[u.country] || []), u ],}),

{});

Intersect

// C#

var targetUsers = usersWhoClicked.Intersect(usersBetween25And45);

// TypeScript

const targetUsers = usersWhoClicked.filter(u => usersBetween25And45.includes(u) // Use a polyfill for IE support);

Last

// C#

var last = users.Last();

// TypeScrip

tif (users.length < 1) {

throw new Error(‘Sequence contains no elements‘);

}

const last = users[users.length - 1];

LastOrDefault

// C#

var last = users.LastOrDefault();

// TypeScript

const last = users[users.length - 1];

Max

// C#

var oldestAge = users.Max(u => u.Age);

// TypeScrip

tif (users.length < 1) {

throw new Error(‘source contains no elements‘);

}

const oldestAge = users.reduce((oa, u) => Math.max(oa, u.age), 0);

Min

// C#

var youngestAge = users.Min(u => u.Age);

// TypeScript

if (users.length < 1) { t

hrow new Error(‘source contains no elements‘);

}

const youngestAge = users.reduce((ya, u) => Math.min(ya, u.age), Number.MAX_VALUE);

OfType

// C#

var bots = users.OfType<Bot>();//根据类型刷新元素

// TypeScript

// No equivalent 无等效项

OrderBy / ThenBy

// C#

var sorted = users.OrderBy(u => u.Age).ThenBy(u => u.Name);

// TypeScript

const sorted = users.sort((a, b) => {

const ageDiff = b.age - a.age;

if (ageDiff)

return ageDiff;

return a.name.localeCompare(b.name);

// Use a polyfill for IE support

}

);

Reverse

// C#

var backwards = users.Reverse();

// TypeScript

const backwards = users.Reverse();// Caution: users is also reversed! 原数组也翻转了

Select

// C#

var names = users.Select(u => u.Name);

// TypeScript

const names = users.map(u => u.name);　　

SelectMany

// C#

var phoneNumbers = users.SelectMany(u => u.PhoneNumbers);

// TypeScript

const phoneNumbers = users.reduce((pn, u) => [ ...pn, ...u.phoneNumbers ], []);　

Single

// C#

var user = users.Single();

// TypeScript

if (users.length > 1) {

throw new Error(‘The input sequence contains more than one element‘);

}else if (!users.length) {

throw new Error(‘The input sequence is empty‘);

}

const user = users[0];

SingleOrDefault

// C#

var user = users.Single();

// TypeScript

const user = users[0];　

Skip

// C#

var otherUsers = users.Skip(n);

// TypeScript

const otherUsers = users.filter((u, i) => i >= n);　

SkipWhile

// C#

var otherUsers = users.SkipWhile(predicate);

// TypeScript

let i = 0;

while (i < users.length && predicate(users[i++]));

const otherUsers = users.slice(i - 1);　

Sum

// C#

var totalYears = users.Sum(u => u.Age);

// TypeScript

if (users.length < 1) {

throw new Error(‘source contains no elements‘);

}

const totalYears = users.reduce((ty, u) => ty + u, 0);

Take

// C#

var otherUsers = users.Take(n);

// TypeScript

const otherUsers = users.filter((u, i) => i < n);

TakeWhile

// C#

var otherUsers = users.TakeWhile(predicate);

// TypeScript

let i = 0;

while (i < users.length && predicate(users[i++]));

const otherUsers = users.slice(0, i - 1);　

Union

// C#

var allUsers = someUser.Union(otherUsers);

// TypeScript

const allUsers = otherUsers.reduce((au, u) =>

au.includes(u) ? au : [ ...au, u ]}), someUsers));// Use a polyfill for IE support

Where

// C#

var adults = users.Where(u => u.Age >= 18);

// TypeScript

const adults = users.filter(u => u.age >= 18);　

Zip

// C#

var matches = buyers.Zip(sellers, (b, s) => new { Buyer = b, Seller = s });

// TypeScript

const matches = []

;for (let i = 0; i < buyers.length && i < sellers.length; i++) {

matches.push({ buyer: buyers[i], seller: sellers[i], });

}

水平有限，请大家见谅，翻译的有误，请指出。谢谢

原文地址 https://decembersoft.com/posts/typescript-vs-csharp-linq/

TypeScript vs. C#: LINQ