简化linq查询？

Question

任何人都可以简化这个非常有效地工作....

FileCompareLength myFileCompare1 = new FileCompareLength(); 
var queryList1Only3 = (from file in list1 select file).Except(list2, myFileCompare1); 
var queryList1Only33 = (from file in list2 select file).Except(list1, myFileCompare1); 
var difference1 = queryList1Only3.ToHashSet(); 
difference1.SymmetricExceptWith(queryList1Only33); 
var query4 = difference1.AsEnumerable().OrderBy(x => x.Name); 
if (query4.Count() > 0) { 
    dest.WriteLine("Discrepancies in File Date:"); 
    foreach (var v in query4) { 
     dest.WriteLine(v.Lengh+ "  " + v.FullName); 
    } 
} 

和

public class FileCompareLength : System.Collections.Generic.IEqualityComparer<System.IO.FileInfo> { 
    public FileCompareLength() { } 
    public bool Equals(System.IO.FileInfo f1, System.IO.FileInfo f2) { 
     return (f1.Length == f2.Length); 
    } 

    public int GetHashCode(System.IO.FileInfo fi) { 
     return fi.Length.GetHashCode(); 
    } 
} 

任何建议？

Answer 1

看来您的目标是获取具有唯一长度的文件列表。如果是这样的话，我会直接去找散列集（如果内存服务的话它会在封面下使用）并跳过LINQ。

var uniqueFiles = new HashSet<FileInfo>(list1, new FileCompareLength()); 
uniqueFiles.SymmetricExceptWith(list2); 
//you should now have the desired list. 
//as mentioned in the comments, check for any items before sorting 
if (uniqueFiles.Any()) 
{ 
    for (var file in uniqueFiles.OrderBy(x => x.Name)) 
    { 
     //do stuff with file 
    } 
} 

如果您使用HashSet的，你也可以利用计，因为它不会涉及遍历整个集合，因为它在你的例子一样，但我觉得，任何传达的意图一样好，是不太可能降低由于其他地方的小变化而表现出色

Answer 2

查看您的代码后，我发现您正在使用繁琐的方法。由于您正在比较FileInfo.Length，我将以int[]为例。比方说：

list1: 1 2 2 5 5 7 (the numbers are lengths of files) 
list2: 2 3 4 7 
list1 except list2(called e1): 1 5 5 
list2 except list1(called e2): 3 4 
SymmetricExceptWith: 1 5 5 3 4 (always e1+e2 because e1/e2 comes from Except) 

这样的代码可以像改善：

var common = list1.Intersect(list2, myFileCompare1); 
var exclusive = list1.Concat(list2).Where(x => !common.Contains(x)) 
            .OrderBy(x => x.Name);