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

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

但是，位于 LINQ 核心的 iE6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();

// 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(); //?.NET 4.0 没找到 找到的是DefaultIfEmpty
//
var  noUsers = IEnumerable.DefaultIfEmpty();

// 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(); //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/