C# 形成两个列表联合的最简单方法
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Simplest way to form a union of two lists
提问by R.S.K
What is the easiest way to compare the elements of two lists say A and B with one another, and add the elements which are present in B to A only if they are not present in A?
比较两个列表的元素（例如 A 和 B）的最简单方法是什么，并且仅当 A 中不存在时才将 B 中存在的元素添加到 A 中？
To illustrate, Take list A = {1,2,3} list B = {3,4,5}
举例说明，取列表 A = {1,2,3} 列表 B = {3,4,5}
So after the operation AUB I want list A = {1,2,3,4,5}
所以在操作 AUB 之后我想要列表 A = {1,2,3,4,5}
采纳答案by Tilak
If it is a list, you can also use AddRangemethod.
如果是列表，也可以使用AddRange方法。
var listB = new List<int>{3, 4, 5};
var listA = new List<int>{1, 2, 3, 4, 5};
listA.AddRange(listB); // listA now has elements of listB also.
If you need new list (and exclude the duplicate), you can use Union
如果您需要新列表（并排除重复项），您可以使用Union
var listB = new List<int>{3, 4, 5};
var listA = new List<int>{1, 2, 3, 4, 5};
var listFinal = listA.Union(listB);
If you need new list (and include the duplicate), you can use Concat
如果您需要新列表（并包含副本），您可以使用Concat
var listB = new List<int>{3, 4, 5};
var listA = new List<int>{1, 2, 3, 4, 5};
var listFinal = listA.Concat(listB);
If you need common items, you can use Intersect.
如果您需要常见项目，您可以使用Intersect。
var listB = new List<int>{3, 4, 5};
var listA = new List<int>{1, 2, 3, 4};
var listFinal = listA.Intersect(listB); //3,4
回答by dasblinkenlight
回答by code4life
I think this is all you really need to do:
我认为这就是你真正需要做的：
var listB = new List<int>{3, 4, 5};
var listA = new List<int>{1, 2, 3, 4, 5};
var listMerged = listA.Union(listB);
回答by Prabhu Murthy
回答by Mikael Engver
If it is two IEnumerable lists you can't use AddRange, but you can use Concat.
如果是两个 IEnumerable 列表，则不能使用AddRange，但可以使用Concat.
IEnumerable<int> first = new List<int>{1,1,2,3,5};
IEnumerable<int> second = new List<int>{8,13,21,34,55};
var allItems = first.Concat(second);
// 1,1,2,3,5,8,13,21,34,55
