C＃中的array.map（）示例？

Consider the following common JavaScript construct

考虑以下常见的JavaScript构造

var ages = people.map(person => person.age);

var ages = people.map（person => person.age）;

Giving the desired result, which is an array of ages.

给出期望的结果，这是一系列的年龄。

What is the equivalent of this in C#? Please include a simple example. The documentation indicates select or possible selectAll but I can't find an example online or any other SO question which can be pasted in and works.

在C＃中，这相当于什么？请举一个简单的例子。文档表明选择或可能selectAll但我找不到在线示例或任何其他可以粘贴和工作的SO问题。

If possible, give an example which turns the following array {1,2,3,4} into the following {'1a','2a','3a','4a'}. For each element, append "a" to the end, turning it from an Integer to a String.

如果可能的话，举一个例子，将下面的数组{1,2,3,4}变成下面的{'1a'，'2a'，'3a'，'4a'}。对于每个元素，在末尾附加“a”，将其从Integer转换为String。

5 个解决方案

#1

This is called projection which is called Select in LINQ. That does not return a new array (like how JavaScript's .map does), but an IEnumerable<T>. You can convert it to an array with .ToArray.

这称为投影，在LINQ中称为Select。这不会返回一个新数组（就像JavaScript的.map一样），而是一个IEnumerable 。您可以使用.ToArray将其转换为数组。

var ages = people.Select(person => person.Age).ToArray();

Select works with all IEnumerable<T> which arrays implement. You just need .NET 3.5 and a using System.Linq; statement.

选择适用于所有IEnumerable 阵列实现的。你只需要.NET 3.5和一个使用System.Linq;声明。

For your 2nd example use something like this. Notice there are no arrays in use - only sequences.

对于你的第二个例子，使用这样的东西。请注意，没有使用数组 - 只有序列。

 var items = Enumerable.Range(1, 4).Select(num => string.Format("{0}a", num));

#2

Only for info, if people is a List<Person>, the ConvertAll method is pretty similar to JS's map, e.g:

仅对于info，如果people是List ，则ConvertAll方法与JS的地图非常相似，例如：

var ages = people.ConvertAll<int>(person => person.age);

But if you have an Array and you want to use any List<T> methods, you can easily achieve that by converting your variable into a List from Array, e.g:

但是如果你有一个数组并且想要使用任何List 方法，你可以通过将变量转换为List中的List来轻松实现这一点，例如：

var ages = people.ToList().ConvertAll<int>(person => person.age);

And finally, if you really need an Array back, then you could convert it back, e.g:

最后，如果你确实需要一个Array，那么你可以将它转换回去，例如：

var ages = people.ToList().ConvertAll<int>(person => person.age).ToArray();

But that last example is not as good as the other answers, and you should use Select if you're working only with Arrays. But if you can, I suggest you to move to List<T>, it's much better!

但是最后一个例子并不像其他答案那么好，如果你只使用Arrays，你应该使用Select。但如果可以的话，我建议你转到List ，它会好得多！

#3

Linq's .Select is the map equivalent and .Aggregate is the fold equivalent.

Linq的.Select是地图的等价物.Aggregate是等效的折叠。

var nums = new[] {1,2,3,4};
string[] r = nums.Select(x => x + "a").ToArray();

#4

The LINQ extension methods on collections give you a host of really handy utilities. Select is one of them:

集合上的LINQ扩展方法为您提供了许多非常方便的实用程序。选择就是其中之一：

int[] arr = { 1, 2, 3 };
IEnumerable<string> list = arr.Select(el => el + "a");
string[] arr2 = list.ToArray();

foreach (var str in arr2)
    Console.Write(str + " ");

This should output:

这应输出：

1a 2a 3a

This can safely be condensed to a 1-liner:

这可以安全地浓缩为1-liner：

string[] arr2 = arr.Select(el => el + "a").ToArray();

A working example:

一个工作的例子：

https://ideone.com/mxxvfy

Related docs:

#5

You can use the keywords from, select, in and while;
Or for your example:

您可以使用关键字from，select，in和while;或者为你的例子：

 var ages = (from person in people select person.age).ToArray();

So essentially the syntax would be:

所以基本上语法是：

 <<list-output>> = (from <<var-name>> in <<list-input>> select <<operation>>);

#1