String.Join忽略空字符串的方法？

Question

VB.NET方法String.Join(separator, stringArray)类似于PHP的内爆,但是数组中的任何null元素都替换为空字符串,因此c:

Dim myArray() as String = { "a", null, "c" }
Console.WriteLine(String.Join(", ", myArray));
// Prints "a, , c"

有一种简单的方法可以将一组字符串与一个忽略空字符串的分隔符连接起来吗？

我不一定需要使用数组或String.Join或其他任何东西.我只需要以下转换:

("a", "b", "c") --> "a, b, c"
("a", null, "c") --> "a, c"

Answer 1

VB.NET

String.Join(",", myArray.Where(Function(s) Not String.IsNullOrEmpty(s)))

C#

String.Join(",", myArray.Where(s => !string.IsNullOrEmpty(s)))

Answer 2

对于C#==> String.Join(",", arr.Where(s => !String.IsNullOrEmpty(s)));

Answer 3

要在 .NET 2.0（无 LINQ）中执行此操作，例如对于 SQL-Server ReportingServices，无需为其编写函数：

网络

Dim a As String = "", b As String = "b", c As String = "", d As String = "d", e As String = ""
Dim lala As String = String.Join(" / ", String.Join(vbBack, New String() {a, b, c, d, e}).Split(New Char() {ControlChars.Back}, System.StringSplitOptions.RemoveEmptyEntries))

System.Console.WriteLine(lala)

C#（适用于从 google 登陆且未搜索 VB.NET 的用户）

string a = "", b = "b", c = "", d = "d", e = "";
string lala = string.Join(" / ",
    string.Join("\u0008", 
        new string[] { a, b, c, d, e }
    ).Split(new char[] { '\u0008' }, System.StringSplitOptions.RemoveEmptyEntries)
);

System.Console.WriteLine(lala);

这假设字符退格键不会出现在您的字符串中（通常应该是这样，因为您不能简单地通过键盘输入该字符）。

另外，如果您从数据库获取值，那就更简单了，因为您可以直接在 SQL 中执行：

PostgreSQL 和 MySQL：

SELECT 
    concat_ws(' / '
        , NULLIF(searchTerm1, '')
        , NULLIF(searchTerm2, '')
        , NULLIF(searchTerm3, '')
        , NULLIF(searchTerm4, '')
    ) AS RPT_SearchTerms; 

即使使用光荣的 MS-SQL-Server，这也是可能的（PS：这是讽刺）：

DECLARE @in_SearchTerm1 nvarchar(100) 
DECLARE @in_SearchTerm2 nvarchar(100) 
DECLARE @in_SearchTerm3 nvarchar(100) 
DECLARE @in_SearchTerm4 nvarchar(100) 

SET @in_SearchTerm1 = N'a'
SET @in_SearchTerm2 = N''
SET @in_SearchTerm3 = N'c'
SET @in_SearchTerm4 = N''

SELECT 
    COALESCE
    (
        STUFF
        (
            (
                SELECT ' / ' + RPT_SearchTerm AS [text()]
                FROM 
                (
                                  SELECT NULLIF(@in_SearchTerm1, N'') AS RPT_SearchTerm, 1 AS RPT_Sort 
                        UNION ALL SELECT NULLIF(@in_SearchTerm2, N'') AS RPT_SearchTerm, 2 AS RPT_Sort  
                        UNION ALL SELECT NULLIF(@in_SearchTerm3, N'') AS RPT_SearchTerm, 3 AS RPT_Sort 
                        UNION ALL SELECT NULLIF(@in_SearchTerm4, N'') AS RPT_SearchTerm, 4 AS RPT_Sort 
                ) AS tempT 
                WHERE RPT_SearchTerm IS NOT NULL 
                ORDER BY RPT_Sort 
                FOR XML PATH(N''), TYPE 
            ).value('.', 'nvarchar(MAX)') 
            ,1
            ,3
            ,N''
        )
        ,N''
    ) AS RPT_SearchTerms 

Answer 4

另一种选择是使用 LINQ 方便的 null 过滤器：

String.Join(",", myArray.OfType<string>())