C＃清单 <string> 包含来自另一个列表的部分匹配 <string>

Question

I have these lists:

var list1 = new List<string>
{
    "BOM_Add",
    "BOM_Edit",
    "BOM_Delete",
    "Paper_Add",
    "Paper_Edit",
    "Paper_Delete"
};

var list2 = new List<string> {"BOM", "Paper_Add"};

I want to create a third list of the common items based on a partial match. So, the third list should contain:

"BOM_Add",
"BOM_Edit",
"BOM_Delete",
"Paper_Add"

because the second list contains "BOM".

If the second list contained "_Edit", then I would expect the third list to have

"BOM_Edit",
"Paper_Edit"

I know how to do this with .Intersect() if I spell out each item (eg "BOM_Add") in the second list, but I need it to be more flexible than that.

Can this be done without iterating through each item on the first list? These lists may get very long and I would prefer to avoid that if I can.

Answer 1

You can use LINQ

var result = list1.Where(r => list2.Any(t => r.Contains(t)))
                  .ToList();

For output:

foreach (var item in result)
{
    Console.WriteLine(item);
}

Output would be:

BOM_Add
BOM_Edit
BOM_Delete
Paper_Add

Can this be done without iterating through each item on the first list?

You have to iterate, either through a loop or using LINQ (which internally iterates as well)

Answer 2

Can this be done without iterating through each item on the first list?

No, if you want to find all of the items that contain one of the items that you have. There is no way of building an index, or any sort of structure that can rule out large sections of items without checking each one. The only option is to compare every single item in the first list with every single item in the other list, doing your Contains check.

If you only needed to do a StartsWith instead of a Contains , then you could sort your list, do a BinarySearch to find the item nearest to the item that you're searching for, which would allow you to easily find all of the items that start with a particular string while only actually needing to check O(log(n) + m) items (where n is the size of the list an m is the average number of matches). You could do the same thing with an EndsWith too, if you just sorted items based on the reverse of the string, but there's no way to sort an items such that a Contains check does this.