计算字符串中的特定字符出现次数

Question

计算字符串中特定字符出现次数的最简单方法是什么？

也就是说,我需要编写一个函数countTheCharacters(),这样

str = "the little red hen"
count = countTheCharacters(str,"e") ' Count should equal 4
count = countTheCharacters(str,"t") ' Count should equal 3

Answer 1

最直接的是简单地遍历字符串中的字符:

Public Function CountCharacter(ByVal value As String, ByVal ch As Char) As Integer
  Dim cnt As Integer = 0
  For Each c As Char In value
    If c = ch Then 
      cnt += 1
    End If
  Next
  Return cnt
End Function

用法:

count = CountCharacter(str, "e"C)

另一种几乎同样有效并且代码更短的方法是使用LINQ扩展方法:

Public Function CountCharacter(ByVal value As String, ByVal ch As Char) As Integer
  Return value.Count(Function(c As Char) c = ch)
End Function

Answer 2

这是一种简单的方法:

text = "the little red hen"
count = text.Split("e").Length -1 ' Equals 4
count = text.Split("t").Length -1 ' Equals 3

Answer 3

你可以试试这个

Dim occurCount As Integer = Len(testStr) - Len(testStr.Replace(testCharStr, ""))

Answer 4

这是一个简单的版本.

text.count(function(x) x = "a")

上面的内容将为您提供字符串中的数字.如果你想忽略大小写:

text.count(function(x) Ucase(x) = "A")

或者,如果你只是想数字:

text.count(function(x) Char.IsLetter(x) = True)

试一试!

Answer 5

或（在 VB.NET 中）：

Function InstanceCount(ByVal StringToSearch As String,
                       ByVal StringToFind As String) As Long
    If Len(StringToFind) Then
        InstanceCount = UBound(Split(StringToSearch, StringToFind))
    End If
End Function

Answer 6

将 Ujjwal Manandhar 的代码转换为 VB.NET 如下...

Dim a As String = "this is test"
Dim pattern As String = "t"
Dim ex As New System.Text.RegularExpressions.Regex(pattern)
Dim m As System.Text.RegularExpressions.MatchCollection
m = ex.Matches(a)
MsgBox(m.Count.ToString())

Answer 7

谢谢，@guffa。能够在一行中完成，甚至在 .NET 中的更长语句中完成，这非常方便。这个 VB.NET 示例计算 LineFeed 字符的数量：

Dim j As Integer = MyString.Count(Function(c As Char) c = vbLf)

j 返回 MyString 中 LineFeed 的数量。