比较两个文本文件并显示什么是相同的

Question

我需要帮助比较两个文件。我能打印出两者之间的区别，但我无法弄清楚如何打印出两者之间的相同之处。有人能帮我吗？提前感谢！

    private void button2_Click(object sender, EventArgs e)
    {
        try
        {
            //Reads files line by line
            var fileOld = File.ReadLines(Old);
            var fileNew = File.ReadLines(New);                              //Ignores cases in files
            IEnumerable<String> OldTxt = fileOld.Except(fileNew, StringComparer.OrdinalIgnoreCase);
            IEnumerable<String> NewTxt = fileNew.Except(fileOld, StringComparer.OrdinalIgnoreCase);

            FileCompare compare = new FileCompare();

            bool areSame = OldTxt.SequenceEqual(NewTxt);

            if (areSame == true)
            {
                MessageBox.Show("They match!");
            }
            else if(areSame == false)
            {
                // Find the set difference between the two files.  
                // Print to Not Equal.txt
                var difFromNew = (from file in OldTxt
                                  select file).Except(NewTxt);

                using (var file = new StreamWriter(NotEqual))
                {
                    foreach (var notEq in difFromNew)
                    {
                        file.WriteLine(notEq.ToString() + "\n", true);
                    }
                }

                MessageBox.Show("They are not the same! Please look at 'Not Equal.txt' to see the difference. Look at 'Equal.txt' to see what is the same at this time.");
            }

        }
        catch
        {
            MessageBox.Show("'NewConvert.txt' or 'OldConvert.txt' files does not exist.");
        }

    }

Answer 1

首先，我认为您的代码中可能有一个bug。“fileOld”包含旧文件的所有内容，而“OldTxt”仅包含新文件中不存在的旧文件文本。在我回答之后，请参阅下面的代码清理想法。

我认为您在寻找Intersect，它返回两个IEnumerables共有的项：

var commonItems = fileOld.Intersect(fileNew);

或者，由于您已经有了在difFromNew中捕获的差异列表，所以您可以再次使用Except：

var difFromNew = fileOld.Except(fileNew); // Note I fixed what I think is a bug here
var commonItems = fileOld.Except(difFromNew);

一些潜在的缺陷：

1. SequenceEqual不仅意味着项目相同，而且它们的顺序也是一样的。如果您关心订单，那么这是合适的。问题是，这将使显示差异变得困难，因为用于比较列表(Except和Intersect) 的其他方法不关心顺序，只关心是否存在项目。因此，如果fileOld包含项cat | dog和fileNew包含项dog | cat，那么它们将不是相等的，但您也无法显示差异(fileOld.Except(fileNew)将包含0项)。
2. 在diffFromNew列表中，您将使用OldTxt (它是旧文件中的唯一文本)，并对NewTxt执行Except，后者是来自新文件的唯一文本。这两者之间不可能有重叠，事实上，OldTxt 默认已经包含了 diffFromNew。

有一种方法可以让你找到你想要的清单：

var oldFilePath = "c:\\oldFile.txt";
var newFilePath = "c:\\newFile.txt";

var oldFileTxt = File.ReadLines(oldFilePath);
var newFileTxt = File.ReadLines(newFilePath);

// Determine if they're equal by checking if there are not any unique items
var filesAreSame = !oldFileTxt.Except(newFileTxt, StringComparer.OrdinalIgnoreCase).Any();

var commonItems = oldFileTxt.Intersect(newFileTxt, StringComparer.OrdinalIgnoreCase);
var uniqueOldItems = oldFileTxt.Except(commonItems, StringComparer.OrdinalIgnoreCase);
var uniqueNewItems = newFileTxt.Except(commonItems, StringComparer.OrdinalIgnoreCase);

下面是代码在这些更改中的表现：

if (filesAreSame)
{
    MessageBox.Show("They match!");
}
else
{
    var commonItems = oldFileTxt.Intersect(newFileTxt, StringComparer.OrdinalIgnoreCase);
    var uniqueOldItems = oldFileTxt.Except(commonItems, StringComparer.OrdinalIgnoreCase);
    var uniqueNewItems = newFileTxt.Except(commonItems, StringComparer.OrdinalIgnoreCase);

    var notEqualsFileText = new StringBuilder();
    if (uniqueOldItems.Any())
    {
        notEqualsFileText.AppendLine(
            $"Entries in {oldFilePath} that are not in {newFilePath}:");
        notEqualsFileText.AppendLine(string.Join(Environment.NewLine, uniqueOldItems));
    }
    if (uniqueNewItems.Any())
    {
        notEqualsFileText.AppendLine(
            $"Entries in {newFilePath} that are not in {oldFilePath}:");
        notEqualsFileText.AppendLine(string.Join(Environment.NewLine, uniqueNewItems));
    }

    File.WriteAllText(notEqualFilePath, notEqualsFileText.ToString());

    var equalsFileText = new StringBuilder();
    if (commonItems.Any())
    {
        equalsFileText.AppendLine(
            $"Entries that are common in both {newFilePath} and {oldFilePath}:");
        equalsFileText.AppendLine(string.Join(Environment.NewLine, commonItems));
    }
    else
    {
        equalsFileText.AppendLine(
            $"There are no common entries in both {newFilePath} and {oldFilePath}.");
    }

    File.WriteAllText(equalFilePath, equalsFileText.ToString());

    MessageBox.Show("The files are not the same! Please look at 'Not Equal.txt' to see the difference. Look at 'Equal.txt' to see what is the same at this time.");
}