加速LINQ对象查询

Question

I am attempting to speed up the following LINQ Object query:

var setOfCodes = codeList1
    .SelectMany(q => q.Codes)
    .Union(codeList2.SelectMany(q => q.Codes)
    .Union(codeList3.SelectMany(q => q.Codes)
    .ToList();

Where

codeListX is a List<Item>

and

public Item {
    public List<int> Codes = new List<int>();
}

Example:

var codeList1 = new List<Item> {
    new Item {
        Codes = new List<int> {
            100,
            105,
            110
        }
    },
    new Item {
        Codes = new List<int> {
            100,
            110,
            115
        }
    },
};
var codeList2 = new List<Item> {
    new Item {
        Codes = new List<int> {
            150,
            155,
            160
        }
    },
    new Item {
        Codes = new List<int> {
            150,
            155,
            170
        }
    },
};

And the output should be (Not fussed about order, I can sort later):

100, 105, 110, 115, 150, 155, 160, 170

IE: Outputs a list containing all the codes that appear within the codeListX 's.

Is there a faster way to do this?

Answer 1

You can write it like this :

var setOfCodes = new[] { codeList1, codeList2, codeList3 }
    .SelectMany(x => x)
    .SelectMany(x => x.Codes)
    .Distinct()
    .ToList();