将“掩码”应用于字符串

Question

我有一个标志枚举（int）掩码，我需要将它转换为表示星期几的字符串。假设这是完整的字符串和任意的掩码。

strFullWeek = "MTWtFSs"
strWeekMask = "0100110"
-----------------------
strResult   = "-T--FS-"

你会提出什么方法来从完整的星期和掩码字符串中获取 strResult？

更新

这是我的“全部上下文”（VB.NET）

<Flags()> Public Enum Week
  Monday = 1
  Tuesday = 2
  Wednesday = 4
  Thursday = 8
  Friday = 16
  Saturday = 32
  Sunday = 64
End Enum

Dim mondayOrSunday = Week.Monday Or Week.Sunday
Dim strDays = "MTWtFSs"

Dim strMondayOrSundayBinary = Convert.ToString(
  mondayOrSunday, 2).PadRight(7, CChar("0"))

Dim charMondayOrSunday = strDays.Zip(
  strMondayOrSundayBinary,
  Function(day, mask) If(mask = CChar("1"), day, CChar("-"))).ToArray()

Dim strMondayOrSunday = New String(charMondayOrSunday)

Console.WriteLine("{0} I see as {1}",
                  mondayOrSunday,
                  strMondayOrSunday)

- serhio

---

你最关心的是什么？速度，可维护性/可读性，还是代码行数最少？ - Steven Doggart

Answer 1

有一个相当简洁的LINQ方法：

var chars = strFullWeek.Zip(strWeekMask, (day, mask) => mask == '1' ? day : '-'))
                       .ToArray();
string text = new string(chars);

虽然这样做效率不高，但可能已经足够了……

编辑：好的，假设您对枚举版本的C#代码感到满意。

// TODO: Rename "Week" to comply with .NET naming conventions
Week mask = Week.Monday | Week.Sunday;
var chars = strFullWeek.Select((value, index) => (int) mask & (1 << index) != 0) 
                                                 ? value : '-')
                       .ToArray();
string text = new string(chars);

- Jon Skeet

---

为了获取 strWeekMask，我使用了 Convert.ToString(myEnum, 2)...也许我可以直接使用枚举？ - serhio

@serhio：很可能是这样。给我们完整的上下文，我们就能给你一个更好的答案。 - Jon Skeet

我有一个标志枚举，代表一周中的每一天。任务是将其转换为可读的字符串（“-T--FS-”）。 - serhio

@serhio：不要“告诉”我们上下文-请将枚举类型编辑到您的问题中。展示您所拥有的“原始”信息。很可能有更好的方法来解决这个问题。 - Jon Skeet

Answer 2

我的快速解决方案使用了StringBuilder。它允许您原地操作字符串。但除非您调用此代码一百万次，否则与LINQ解决方案相比，您不会注意到任何速度差异。

string strFullWeek = "MTWtFSs";
string strWeekMask = "0100110";

var sb = new StringBuilder(strFullWeek);
for (int i = 0; i < strWeekMask.Length; i++) {
    if (strWeekMask[i] == '0') {
        sb[i] = '-';
    }
}
string result = sb.ToString();

- Olivier Jacot-Descombes

Answer 3

请看下文：

var strFullWeek = "MTWtFSs";
var strWeekMask = "0100110";

var strFullWeekArray = strFullWeek.ToList();
var strWeekMaskArray = strWeekMask.ToList();

Console.WriteLine(string.Join(
    string.Empty,
    strFullWeek.Select(c => (strWeekMaskArray[strFullWeekArray.IndexOf(c)] == '1')
        ? c
        : '-')));

- Mike Perrenoud

Answer 4

如果你想要更易读的选项，这里有一个替代方案：

string fullWeek = "MTWtFSs";
string weekMask = "0100110";

const char blankChar = '-';

int totalChars = fullWeek.Length;

StringBuilder result = new StringBuilder();

for (int index = 0; index < totalChars; index++)
{
    if (weekMask[index] == '1')
    {
        result.Append(fullWeek[index]);
    }
    else
    {
        result.Append(blankChar);
    }
}

Console.WriteLine(result);

- Adrian Thompson Phillips

Answer 5

虽然我来晚了，但是我想尝试一下。这是我的非常规 LINQ 方法：

var result = new string(strFullWeek.Select((letter, index) 
                         => strWeekMask[index] == '1' ? letter : '-').ToArray());

- Rob P.

Answer 6

如果您想直接使用枚举，可以像这样操作：

[Flags()]
enum Week
{
    Monday = 1,
    Tuesday = 2,
    Wednesday = 4,
    Thursday = 8,
    Friday = 16,
    Saturday = 32,
    Sunday = 64
}

const string strFullWeek = "MTWtFSs";

string GetMaskedWeek(Week days)
{
    char[] result = new char[strFullWeek.Length];
    for (int i = 0; i < strFullWeek.Length; i++)
    {
        if ((((int)days >> i) & 1) != 0)
            result[i] = strFullWeek.ToCharArray(i, 1)[0];
        else
            result[i] = '-';
    }
    return new string(result);
}

或者，在VB.NET中：

<Flags()> Public Enum Week
    Monday = 1
    Tuesday = 2
    Wednesday = 4
    Thursday = 8
    Friday = 16
    Saturday = 32
    Sunday = 64
End Enum

Dim strFullWeek As String = "MTWtFSs"

Private Function GetMaskedWeek(ByVal days As Week) As String
    Dim result(strFullWeek.Length) As Char
    For i As Integer = 0 To strFullWeek.Length - 1
        If ((days >> i) And 1) <> 0 Then
            result(i) = strFullWeek.ToCharArray(i, 1)(0)
        Else
            result(i) = "-"c
        End If
    Next
    Return New String(result)
End Function

- Steven Doggart

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这实际上是我最初的代码，但我将其更新以匹配问题中的枚举，其中星期四为16 :) - Steven Doggart