TypeScript vs. C#: LINQ

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）。

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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

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// C# var leftToRight = users.Aggregate(initialValue, (a, u) => /* ... */);    // TypeScript const leftToRight = users.reduce((a, u) => /* ... */, initialValue); const rightToLeft = users.reduceRight((a, u) => /* ... */, initialValue);

All

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// C# var allReady = users.All(u => u.IsReady);    // TypeScrip tconst allReady = users.every(u => u.isReady);

Any

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// C# var isDirty = users.Any(u => u.IsDirty);    // TypeScript const isDirty = users.some(u => u.isDirty);

Append

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// C# var allUsers = users.Append(oneMoreUser);    // TypeScript const allUsers = [ ...users, oneMoreUser ];

Average

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// 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

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// 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

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// C# var allUsers = users.Concat(moreUsers);    // TypeScript const allUsers = [ ...users, ...moreUsers ];

Contains

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// C# var hasAdmin = users.Contains(admin);    // TypeScript const hasAdmin = users.includes(admin); // Use a polyfill for IE support

Count

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// C# var n = users.Count();    // TypeScript const n = users.length;

DefaultIfEmpty

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// C# var nonEmptyUsers = Enumerable.DefaultIfEmpty(users);    // TypeScript const nonEmptyUsers = users.length ? users : [ null ];

Distinct

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// 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

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// 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

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// C# var nth = users.ElementAtOrDefault(n);    // TypeScript const nth = users[n];

Empty

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// 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

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// 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

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// C# var first = users.First();    // TypeScript if (users.length < 1) {  throw new Error('Sequence contains no elements'); } const first = users[0];

FirstOrDefault

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// C# var first = users.FirstOrDefault();    // TypeScript const first = users[0];

List.ForEach

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// C# users.ToList().ForEach(u => /* ... */);    // TypeScript users.forEach(u => /* ... */);

GroupBy

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// C# var usersByCountry = users.GroupBy(u => u.Country);    // TypeScript const usersByCountry = users.reduce((ubc, u) => ({  ...ubc,  [u.country]: [ ...(ubc[u.country] || []), u ],}), {});

Intersect

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

Last

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// C# var last = users.Last();    // TypeScrip tif (users.length < 1) {  throw new Error('Sequence contains no elements'); } const last = users[users.length - 1];

LastOrDefault

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// C# var last = users.LastOrDefault();    // TypeScript const last = users[users.length - 1];

Max

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// 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

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// 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

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// C# var bots = users.OfType<Bot>();//根据类型刷新元素    // TypeScript // No equivalent   无等效项

OrderBy / ThenBy

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// 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

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

Select

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// C# var names = users.Select(u => u.Name);    // TypeScript const names = users.map(u => u.name);

SelectMany

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// C# var phoneNumbers = users.SelectMany(u => u.PhoneNumbers);    // TypeScript const phoneNumbers = users.reduce((pn, u) => [ ...pn, ...u.phoneNumbers ], []);

Single

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// 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

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// C# var user = users.Single();    // TypeScript const user = users[0];

Skip

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// C# var otherUsers = users.Skip(n);    // TypeScript const otherUsers = users.filter((u, i) => i >= n);

SkipWhile

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// C# var otherUsers = users.SkipWhile(predicate);    // TypeScript let i = 0; while (i < users.length && predicate(users[i++]));    const otherUsers = users.slice(i - 1);

Sum

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// 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

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// C# var otherUsers = users.Take(n);    // TypeScript const otherUsers = users.filter((u, i) => i < n);

TakeWhile

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// 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

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// 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

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// C# var adults = users.Where(u => u.Age >= 18);    // TypeScript const adults = users.filter(u => u.age >= 18);

Zip

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// 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/