如何在 c# 條件下從 object 列表中刪除所有下一個元素

Question

我有一個對象列表

public class Card
{
    public int Id { get; set; }
    public double Price { get; set; }
    public string Name{ get; set; }
}

當條件匹配時如何從列表中刪除所有下一個元素 -

if(object1.Price== 0)
{
  //remove all next elements from list
}

我想將列表從 0 保持到匹配 position 就像如果價格在索引 5 處為零，則取 0 到 5 個元素。

Answer 1

您可以使用TakeWhile和Select的組合，例如：

var lst = new List<Card>()      {
     new Card() { Price = 2 },
     new Card() { Price = 1 },
     new Card() { Price = 0 },
     new Card() { Price = -1 },
     new Card() { Price = -2 },         
};
var found = false;      
var items = lst.TakeWhile(x => !found).Select(x => 
{
    if (x.Price == 0)
        found = true;
    return x;
});

這導致價格為 2、1、0 的項目被保留，而 -1 和 -2 被刪除。

請參閱此小提琴進行測試。

Answer 2

如果您使用List<T>其中T是Card您可以使用List<T>.FindIndex來獲取與謂詞匹配的第一個元素的索引並獲取列表的范圍：

List<Card> cards = new List<Card> { new Card {Id = 1, Price = 1.0, Name = "Ace" }, 
new Card {Id = 2, Price = 0.0, Name="Two" }};
Predicate<Card> test1 = a => a.Price == 1.0;
Predicate<Card> test2 = b => b.Price == 0.0;
//You can also do something like this:
Predicate<Card> test3 = c => c.Price == 1.0 && c.Id == 1;


Console.WriteLine(GetCardRange(cards, test1).Count); //Prints 1
Console.WriteLine(GetCardRange(cards, test2).Count); //Prints 2
Console.WriteLine(GetCardRange(cards, test3).Count); //Prints 1

//or shorthand without declaring a Predicate:
Console.WriteLine(GetCardRange(cards, (a) => a.Price == 0.0).Count); //Prints 2


//Method accepts a predicate so you can pass in different
//types of condition(s)
public List<Card> GetCardRange(List<Card> cards, Predicate<Card> p)
{
    int index = cards.FindIndex(p);
    //if no card is found, either return the whole list 
    //or change to return null or empty list
    return index == -1 ? cards : 
       cards.GetRange(0, index + 1);
}

public class Card
{
    public int Id { get; set; }
    public double Price { get; set; }
    public string Name{ get; set; }
}