C# 从列表中选择随机元素
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C# Select random element from List
提问by Rick Velt
I am creating a little quiz console application. I have made a list with 3 questions in it. How can I let the program randomly select a question and print it out int the console?
我正在创建一个小测验控制台应用程序。我列了一个清单，里面有 3 个问题。如何让程序随机选择一个问题并在控制台中打印出来？
I have tried some different codes but can't seem the get it working for some reason. This is the last code I tried, which I got from another user from this site, but I get the errors:
我尝试了一些不同的代码，但由于某种原因似乎无法使其正常工作。这是我尝试的最后一个代码，这是我从该站点的另一个用户那里获得的，但出现错误：
The name 'string' does not exist in the current context.
当前上下文中不存在名称“字符串”。
"Since Quiz.Questions.main()returns void, a return keyword must not be followed by an object expression".
“由于Quiz.Questions.main()返回void，返回关键字后不能跟对象表达式”。
Here is the last piece of code which I tried:
这是我尝试的最后一段代码：
class Questions
{
public static void main()
{
var questions = new List<string>{
"question1",
"question2",
"question3"};
int index = Random.Next(strings.Count);
questions.RemoveAt(index);
return questions;
}
}
}
Thank you all for your responses. I have fixed my problem by creating an array instead of an List. This is my code now :
谢谢大家的回复。我通过创建一个数组而不是一个列表来解决我的问题。这是我现在的代码：
class Questions
{
public static void main()
{
string[] questions = new string[3];
questions[0] = "question1";
questions[1] = "question2";
questions[2] = "question3";
Random rnd = new Random();
Console.WriteLine(questions[rnd.Next(0,2)]);
}
}
回答by Bill Gregg
You need a System.Console.WriteLine statment.
您需要一个 System.Console.WriteLine 语句。
class Questions
{
public static void main()
{
var questions = new List<string>{
"question1",
"question2",
"question3"};
int index = Random.Next(questions.Count);
System.Console.WriteLine(questions[index]);
}
}
回答by Tim Schmelter
"The name 'string' does not exists in current context"
“当前上下文中不存在名称‘字符串’”
I assume you want
我假设你想要
int index = random.Next(questions.Count); // according to the lower-case random see last paragraph
instead of
代替
int index = Random.Next(strings.Count);
Since there is no variable with the name stringsand you want to remove one question anyway.
由于名称中没有变量，strings您无论如何都想删除一个问题。
Also, you cannot return something from a voidmethod. So create one that returns the list:
此外，您不能从void方法中返回某些内容。所以创建一个返回列表的：
private Random random = new Random();
List<string> GetRemoveQuestion(List<string> questions)
{
int index = random.Next(questions.Count);
questions.RemoveAt(index);
return questions;
}
Edit: last but not least, you cannot use Random.Next. That would presume that there is a staticNextmethod in Randomwhich is not the case. Therefore i have shown above how you create and use an instance. Note that you should not create it i the method itself since it is seeded with the curent time. If you'd call this method very fast you'd get the same "random" value often.
编辑：最后但并非最不重要的是，您不能使用Random.Next. 这将假定有一个staticNext在方法Random是不是这样的。因此，我已经在上面展示了如何创建和使用实例。请注意，您不应该在方法本身中创建它，因为它是用当前时间播种的。如果您非常快速地调用此方法，您将经常获得相同的“随机”值。
Have a look at msdn at the remarks sectionfor more details.
回答by Jonas W
Are you sure that you want to remove a question and return the rest of the questions? Should you not only select one? Somthing like this :
您确定要删除一个问题并返回其余问题吗？你不应该只选择一个吗？像这样的东西：
public static void main()
{
var random = new Random();
var questions = new List<string>{
"question1",
"question2",
"question3"};
int index = random.Next(questions.Count);
Console.WriteLine(questions[index]);
}
回答by Tom Chantler
You have a couple of minor errors.
你有几个小错误。
You need a reference to a Randobject. You are looking at stringsinstead of questions. You are removing an element instead of selecting it.
你需要一个Rand对象的引用。您正在查看strings而不是questions. 您正在删除一个元素而不是选择它。
Try this:
尝试这个：
void Main()
{
Random rand = new Random();
var questions = new List<string>{
"question1",
"question2",
"question3"};
int index = rand.Next(questions.Count);
return questions[index];
// If you want to use Linq then
// return questions.Skip(index).Take(1);
}
回答by Theodoros Chatzigiannakis
Something like this could be what you want:
这样的事情可能是你想要的：
private Random rng;
T PickRandom<T>(List<T> list)
{
return list[rng.NextInt(list.Count)];
}
You can call it on your list to get a random element from it.
您可以在列表中调用它以从中获取随机元素。
回答by Kami
Try something like this
尝试这样的事情
public static void main()
{
var questions = new List<string>{
"question1",
"question2",
"question3"};
Random rnd = new Random();
int index = rnd.Next(questions.Count)
string question = questions[index];
questions.RemoveAt(index); // Are you sure you neex to remove?
System.Console.WriteLine(question);
}
There is a typo in where you are using stringinstead of questions. Also, Randomobject needs to be initalised.
您使用的地方有一个错字，string而不是questions。此外，Random对象需要被初始化。
回答by JJ_Coder4Hire
For other searchers benefit: If you want a depleting list so you ensure you use all items in a random fashion then do this:
对于其他搜索者的好处：如果您想要一个耗尽列表以确保以随机方式使用所有项目，请执行以下操作：
//use the current time to seed random so it's different every time we run it
Random rand = new Random(DateTime.Now.ToString().GetHashCode());
var list = new List<string>{ "item1", "item2", "item3"};
//keep extracting from the list until it's depleted
while (list.Count > 0) {
int index = rand.Next(0, list.Count);
Console.WriteLine("Rand Item: " + list[index]);
list.RemoveAt(index);
}
