C# LINQ学习笔记三：LINQ to OBJECT之操作字符串

class Program
{
static void Main(string[] args)
{
#region LINQ 统计单词在字符串中出现的次数
const string text = @"Historically, the world of data and the world of objects" +
@" have not been well integrated. Programmers work in C# or Visual Basic" +
@" and also in SQL or XQuery. On the one side are concepts such as classes," +
@" objects, fields, inheritance, and .NET Framework APIs. On the other side" +
@" are tables, columns, rows, nodes, and separate languages for dealing with" +
@" them. Data types often require translation between the two worlds; there are" +
@" different standard functions. Because the object world has no notion of query, a" +
@" query can only be represented as a string without compile-time type checking or" +
@" IntelliSense support in the IDE. Transferring data from SQL tables or XML trees to" +
@" objects in memory is often tedious and error-prone.";
const string searchWord = "data"; //字符串转换成数组
var source = text.Split(new[] { '.', '?', '!', ' ', ';', ':', ',' }, StringSplitOptions.RemoveEmptyEntries); //创建查询，并忽略大小写比较。
var query = from word in source
where string.Equals(word, searchWord, StringComparison.InvariantCultureIgnoreCase)
select word; //统计匹配数量
var wordCount = query.Count();
Console.WriteLine($"{wordCount} occurrences(s) of the search word \"{searchWord}\" were found.");
Console.Read();
#endregion
}
}

class Program
{
static void Main(string[] args)
{
#region LINQ 查询包含指定一组单词的句子
const string text = @"Historically, the world of data and the world of objects " +
@"have not been well integrated. Programmers work in C# or Visual Basic " +
@"and also in SQL or XQuery. On the one side are concepts such as classes, " +
@"objects, fields, inheritance, and .NET Framework APIs. On the other side " +
@"are tables, columns, rows, nodes, and separate languages for dealing with " +
@"them. Data types often require translation between the two worlds; there are " +
@"different standard functions. Because the object world has no notion of query, a " +
@"query can only be represented as a string without compile-time type checking or " +
@"IntelliSense support in the IDE. Transferring data from SQL tables or XML trees to " +
@"objects in memory is often tedious and error-prone."; //将文本块切割成数组
var sentences = text.Split('.', '?', '!'); //定义搜索条件，此列表可以在运行时动态添加。
string[] wordsToMatch = { "Historically", "data", "integrated" }; var query = from sentence in sentences
let t = sentence.Split(new char[] { '.', '?', '!', ' ', ';', ':', ',' }, StringSplitOptions.RemoveEmptyEntries)
where t.Distinct().Intersect(wordsToMatch).Count() == wordsToMatch.Length //去重，取交集后的数量对比。
select sentence; foreach (var sentence in query)
{
Console.WriteLine(sentence);
}
Console.Read();
#endregion
}
}

class Program
{
static void Main(string[] args)
{
#region LINQ 在字符串中查询字符
const string source = "ABCDE99F-J74-12-89A"; //只选择数字的字符
var digits = from character in source
where char.IsDigit(character)
select character;
Console.Write("Digit:");
foreach (var digit in digits)
{
Console.Write($"{digit} ");
}
Console.WriteLine(); //选择第一个"-"之前的所有字符
var query = source.TakeWhile(x => x != '-');
foreach (var character in query)
{
Console.Write(character);
} Console.Read();
#endregion
}
}

class Program
{
static void Main(string[] args)
{
#region LINQ 正则表达式结合LINQ查询
//请根据不同版本的VS进行路径修改
const string floder = @"C:\Program Files (x86)\Microsoft Visual Studio\";
var fileInfoes = GetFiles(floder);
//创建正则表达式来寻找所有的"Visual"
var searchTerm = new Regex(@"http://(www.w3.org|www.npmjs.org)"); //搜索每一个“.html”文件
//通过where找到匹配项
//注意：select中的变量要求显示声明其类型，因为MatchCollection不是泛型IEnumerable集合。
var query = from fileInfo in fileInfoes
where fileInfo.Extension == ".html"
let text = File.ReadAllText(fileInfo.FullName)
let matches = searchTerm.Matches(text)
where matches.Count >
select new
{
name = fileInfo.FullName,
matchValue = from Match match in matches select match.Value
}; Console.WriteLine($"The term \"{searchTerm}\" was found in:");
Console.WriteLine();
foreach (var q in query)
{
//修剪匹配找到的文件中的路径
Console.WriteLine($"name==>{q.name.Substring(floder.Length - 1)}");
//输出找到的匹配值
foreach (var v in q.matchValue)
{
Console.WriteLine($"matchValue==>{v}");
}
//输出空白行
Console.WriteLine();
}
Console.Read();
#endregion
} /// <summary>
/// 获取指定路径的文件信息
/// </summary>
/// <param name="path"></param>
/// <returns></returns>
private static IList<FileInfo> GetFiles(string path)
{
var files = Directory.GetFiles(path, "*.*", SearchOption.AllDirectories); return files.Select(file => new FileInfo(file)).ToList();
}
}

Bankov, Peter
Holm, Michael
Garcia, Hugo
Potra, Cristina
Noriega, Fabricio
Aw, Kam Foo
Beebe, Ann
Toyoshima, Tim
Guy, Wey Yuan
Garcia, Debra

Liu, Jinghao
Bankov, Peter
Holm, Michael
Garcia, Hugo
Beebe, Ann
Gilchrist, Beth
Myrcha, Jacek
Giakoumakis, Leo
McLin, Nkenge
El Yassir, Mehdi

class Program
{
static void Main(string[] args)
{
#region LINQ 查找两个集合间的差异
//创建数据源
var text1 = File.ReadAllLines(@"..\..\text1.txt");
var text2 = File.ReadAllLines(@"..\..\text2.txt"); //创建查询，这里必须使用方法语法。
var query = text1.Except(text2); //执行查询
Console.WriteLine("The following lines are in text1.txt but not text2.txt");
foreach (var name in query)
{
Console.WriteLine(name);
}
Console.Read();
#endregion
}
}

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class Program
{
static void Main(string[] args)
{
#region LINQ 排序或过滤任意单词或字段的文本数据
//创建数据源
var scores = File.ReadAllLines(@"..\..\scores.csv");
//可以改为0~4的任意值
const int sortIndex = ;
//演示从方法返回查询变量，非查询结果。
foreach (var score in SplitSortQuery(scores, sortIndex))
{
Console.WriteLine(score);
}
Console.Read();
#endregion
} /// <summary>
/// 分割字符串排序
/// </summary>
/// <param name="scores"></param>
/// <param name="num"></param>
/// <returns></returns>
private static IEnumerable<string> SplitSortQuery(IEnumerable<string> scores, int num)
{
var query = from line in scores
let fields = line.Split(',')
orderby fields[num] descending
select line;
return query;
}
}

Adams,Terry,
Fakhouri,Fadi,
Feng,Hanying,
Garcia,Cesar,
Garcia,Debra,
Garcia,Hugo,
Mortensen,Sven,
O'Donnell,Claire,112
Omelchenko,Svetlana,
Tucker,Lance,
Tucker,Michael,
Zabokritski,Eugene,

class Program
{
static void Main(string[] args)
{
#region LINQ 对一个分割的文件的字段重新排序
//数据源
var lines = File.ReadAllLines(@"..\..\spread.csv");
//将旧数据的第2列的字段放到第一位，逆向结合第0列和第1列的字段。
var query = from line in lines
let t = line.Split(',')
orderby t[]
select $"{t[2]} {t[1]} {t[0]}"; foreach (var item in query)
{
Console.WriteLine(item);
}
Console.Read();
#endregion
}
}

class Program
{
static void Main(string[] args)
{
#region LINQ 组合和比较字符串集合
var text1 = File.ReadAllLines(@"..\..\text1.txt");
var text2 = File.ReadAllLines(@"..\..\text2.txt"); //简单连接并排序，重复保存。
var concatQuery = text1.Concat(text2).OrderBy(x => x);
OutputQueryResult(concatQuery, "Simple concatenate and sort,duplicates are preserved:"); //基于默认字符串比较器连接，并删除重名。
var unionQuery = text1.Union(text2).OrderBy(x => x);
OutputQueryResult(unionQuery, "Union removes duplicate names:"); //查找在两个文件中出现的名称
var intersectQuery = text1.Intersect(text2).OrderBy(x => x);
OutputQueryResult(intersectQuery, "Merge based on intersect:"); //在每个列表中找到匹配的字段，使用concat将两个结果合并，然后使用默认的字符串比较器进行排序。
const string nameMatch = "Garcia";
var matchQuery1 = from name in text1
let t = name.Split(',')
where t[] == nameMatch
select name;
var matchQuery2 = from name in text2
let t = name.Split(',')
where t[] == nameMatch
select name;
var temp = matchQuery1.Concat(matchQuery2).OrderBy(x => x);
OutputQueryResult(temp, $"Concat based on partial name match \"{nameMatch}\":"); Console.Read();
#endregion
} /// <summary>
/// 输出查询结果
/// </summary>
/// <param name="querys"></param>
/// <param name="title"></param>
private static void OutputQueryResult(IEnumerable<string> querys, string title)
{
Console.WriteLine(Environment.NewLine + title);
foreach (var query in querys)
{
Console.WriteLine(query);
}
Console.WriteLine($"Total {querys.Count()} names in list.");
}
}

class Program
{
static void Main(string[] args)
{
#region LINQ 从多个源中填充对象集合
//spread.csv每行包含姓氏、名字和身份证号，以逗号分隔。例如，Omelchenko,Svetlana,111
var names = File.ReadAllLines(@"..\..\spread.csv");
//scores.csv每行包括身份证号码和四个测试评分，以逗号分隔。例如，111，97，92，81，60
var scores = File.ReadAllLines(@"..\..\scores.csv"); //使用一个匿名的类型合并数据源。
//注：动态创建一个int的考试成绩成员列表。
//跳过分割字符串中的第一项，因为它是学生的身份证，不是一个考试成绩。
var students = from name in names
let t1 = name.Split(',')
from score in scores
let t2 = score.Split(',')
where t1[] == t2[]
select new
{
FirstName = t1[],
LastName = t1[],
ID = Convert.ToInt32(t1[]),
ExamScores = (from score in t2.Skip() select Convert.ToInt32(score)).ToList()
}; foreach (var student in students)
{
Console.WriteLine($"The average score of {student.FirstName} {student.LastName} is {student.ExamScores.Average()}.");
}
Console.Read();
#endregion
}
}

class Program
{
static void Main(string[] args)
{
#region LINQ 使用group将一个文件拆分成多个文件
var text1 = File.ReadAllLines(@"..\..\text1.txt");
var text2 = File.ReadAllLines(@"..\..\text2.txt"); //并集：连接并删除重复的名字
var mergeQuery = text1.Union(text2);
//根据姓氏的首字母对姓名进行分组
var query = from name in mergeQuery
let t = name.Split(',')
group name by t[][] into g
orderby g.Key
select g; //注意嵌套的 foreach 循环
foreach (var g in query)
{
var fileName = @"testFile_" + g.Key + ".txt";
Console.WriteLine(g.Key + ":"); //写入文件
using (var sw = new StreamWriter(fileName))
{
foreach (var name in g)
{
sw.WriteLine(name);
Console.WriteLine(" " + name);
}
}
}
Console.Read();
#endregion
}
}

class Program
{
static void Main(string[] args)
{
#region LINQ 向不同的文件中加入内容
var names = File.ReadAllLines(@"..\..\spread.csv");
var scores = File.ReadAllLines(@"..\..\scores.csv"); //该查询基于ID连接两个不同的电子表格
var query = from name in names
let t1 = name.Split(',')
from score in scores
let t2 = score.Split(',')
where t1[] == t2[]
orderby t1[]
select $"{t1[0]},{t2[1]},{t2[2]},{t2[3]},{t2[4]}"; //输出
OutputQueryResult(query, "Merge two spreadsheets:");
Console.Read();
#endregion
} /// <summary>
/// 输出查询结果
/// </summary>
/// <param name="querys"></param>
/// <param name="title"></param>
private static void OutputQueryResult(IEnumerable<string> querys, string title)
{
Console.WriteLine(Environment.NewLine + title);
foreach (var query in querys)
{
Console.WriteLine(query);
}
Console.WriteLine($"Total {querys.Count()} names in list.");
}
}

class Program
{
static void Main(string[] args)
{
#region LINQ 计算一个CSV文本文件中的列值
var scores = File.ReadAllLines(@"..\..\scores.csv"); //指定要计算的列
const int examNum = ; //+1表示跳过第一列
//统计单列
SingleColumn(scores, examNum + ); Console.WriteLine(); //统计多列
MultiColumns(scores); Console.Read();
#endregion
} /// <summary>
/// 统计单列
/// </summary>
/// <param name="lines"></param>
/// <param name="examNum"></param>
private static void SingleColumn(IEnumerable<string> lines, int examNum)
{
Console.WriteLine("Single Column Query:"); //查询步骤：
//1.分割字符串
//2.对要计算的列的值转换为int
var query = from line in lines
let t = line.Split(',')
select Convert.ToInt32(t[examNum]); //对指定的列进行统计
var average = query.Average();
var max = query.Max();
var min = query.Min(); Console.WriteLine($"Exam #{examNum}: Average:{average:##.##} High Score:{max} Low Score:{min}");
} /// <summary>
/// 统计多列
/// </summary>
/// <param name="lines"></param>
private static void MultiColumns(IEnumerable<string> lines)
{
Console.WriteLine("Multi Column Query:"); //查询步骤：
//1.分割字符串
//2.跳过ID列（第一列）
//3.将当前行的每个评分都转换成int，并选择整个序列作为一行结果。
var query1 = from line in lines
let t1 = line.Split(',')
let t2 = t1.Skip()
select (from t in t2 select Convert.ToInt32(t)); //执行查询并缓存结果以提高性能
var results = query1.ToList();
//找出结果的列数
var count = results[].Count(); //执行统计
for (var i = ; i < count; i++)
{
var query2 = from result in results
select result.ElementAt(i);
var average = query2.Average();
var max = query2.Max();
var min = query2.Min();
//#1表示第一次考试
Console.WriteLine($"Exam #{i + 1} Average: {average:##.##} High Score: {max} Low Score: {min}");
} }
}