在 C# 中删除项目时进行 HashSet 迭代
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HashSet Iterating While Removing Items in C#
提问by aHunter
I have a hashset in C# that I'm removing from if a condition is met while iterating though the hashset and cannot do this using a foreach loop as below.
我在 C# 中有一个哈希集，如果在迭代哈希集时满足条件，我将删除它，并且不能使用如下的 foreach 循环来执行此操作。
foreach (String hashVal in hashset)
{
if (hashVal == "somestring")
{
hash.Remove("somestring");
}
}
So, how can I remove elements while iterating?
那么，如何在迭代时删除元素？
采纳答案by adrianbanks
Use the RemoveWheremethod of HashSet instead:
改用HashSet的RemoveWhere方法：
hashset.RemoveWhere(s => s == "somestring");
You specify a condition/predicate as the parameter to the method. Any item in the hashset that matches the predicate will be removed.
您指定一个条件/谓词作为方法的参数。哈希集中与谓词匹配的任何项目都将被删除。
This avoids the problem of modifying the hashset whilst it is being iterated over.
这避免了在迭代时修改哈希集的问题。
In response to your comment:
回应你的评论：
's' represents the current item being evaluated from within the hashset.
's' 表示从哈希集中评估的当前项目。
The above code is equivalent to:
上面的代码等价于：
hashset.RemoveWhere(delegate(string s) {return s == "somestring";});
or:
或者：
hashset.RemoveWhere(ShouldRemove);
public bool ShouldRemove(string s)
{
return s == "somestring";
}
EDIT:Something has just occurred to me: since HashSet is a set that contains no duplicate values, just calling hashset.Remove("somestring")will suffice. There is no need to do it in a loop as there will never be more than a single match.
编辑：我刚刚发生了一些事情：由于 HashSet 是一个不包含重复值的集合，因此只需调用hashset.Remove("somestring")就足够了。没有必要在循环中进行，因为永远不会超过一个匹配项。
回答by Nescio
Usually when I want to iterate over something and remove values I use:
通常当我想迭代某些东西并删除我使用的值时：
For (index = last to first)
If(ShouldRemove(index)) Then
Remove(index)
回答by Fredrik M?rk
You can't remove items from a collection while looping over it with an enumerator. Two approaches to solve this are:
在使用枚举器循环遍历集合时，您无法从集合中删除项目。解决这个问题的两种方法是：
- Loop backwards over the collection using a regular indexed for-loop (which I believe is not an option in the case of a
HashSet) - Loop over the collection, add items to be removed to another collection, then loop over the "to-be-deleted"-collection and remove the items:
- 使用常规索引 for 循环在集合上向后循环（我认为在 a 的情况下不是一个选项
HashSet） - 循环遍历集合，将要删除的项目添加到另一个集合，然后遍历“待删除”集合并删除项目：
Example of the second approach:
第二种方法的例子：
HashSet<string> hashSet = new HashSet<string>();
hashSet.Add("one");
hashSet.Add("two");
List<string> itemsToRemove = new List<string>();
foreach (var item in hashSet)
{
if (item == "one")
{
itemsToRemove.Add(item);
}
}
foreach (var item in itemsToRemove)
{
hashSet.Remove(item);
}
回答by javapowered
I would avoid using two foreach loop - one foreach loop is enough:
我会避免使用两个 foreach 循环——一个 foreach 循环就足够了：
HashSet<string> anotherHashSet = new HashSet<string>();
foreach (var item in hashSet)
{
if (!shouldBeRemoved)
{
anotherSet.Add(item);
}
}
hashSet = anotherHashSet;
