Replace {#Text} and {$Text} in a string, in a performant way

Question

NOTE: This is not a simple string replace question.

SomethingBlahBlah can be #SomeThingOtherthanThis

My case is as follows, I have a large string (<1024B, but >300B), that will have {#String} and {$String}.

To be more specific {#SomethingBlahBlah} and {$SomeOtherThingBlahBlah}, so in regexp {#w+} and {$w+}

My first question is, are regexps the only way to do it? I'd love a string replace solution or such, and secondly if it is, is there a way to just do one compiled regex and do a single pass through?

Can Linq help by any chance?

Answer 1

String.Replace("SomethingBlahBlah", "SomeOtherThingBlahBlah")

Edit: Just found a great answer by Jon Skeet in this thread.

Answer 2

Regex takes more time to replace text instead of using String.Replace method. But Regex give you a huge power with text manipulation. LINQ hasn't a direct methods to work with string. It only can use existing features.

Answer 3

For a large string, and several different replacements, I would recommend using StringBuilder.

StringBuilder sb = new StringBuilder(input);
sb.Replace("{$String}", "Real Value");
sb.Replace("{$SomeOtherThingBlahBlah}", "Another Real Value");
return sb.ToString();

Manipulations will happen in memory, and a new string will not be allocated until you call ToString().

Answer 4

You can use one of these:

Option 1

Regex:

\{(?:#|\$)(\w+)}

Text:

{#SomethingBlahBlah} and {$SomeOtherThingBlahBlah}

Returns:

Result 1

   1. SomethingBlahBlah

Result 2

   1. SomeOtherThingBlahBlah

Option 2

Regex:

(\{(?:#|\$)(?:\w+)})

Text:

{#SomethingBlahBlah} and {$SomeOtherThingBlahBlah}

Returns:

Result 1

   1. {#SomethingBlahBlah}

Result 2

   1. {$SomeOtherThingBlahBlah}

Answer 5

IndexOf vs Regex: Tested using Stopwatch ticks over 100000 iterations with 500~ length string.

Method IndexOf

public static string Re(string str)
{
    int strSIndex = -1;
    int strEIndex = -1;

    strSIndex = str.IndexOf("{#");
    if (strSIndex == -1) strSIndex = str.IndexOf("{$");
    if (strSIndex == -1) return str;

    strEIndex = str.IndexOf("}");
    if (strEIndex == -1) return str;

    if (strEIndex < strSIndex)
    {
        strSIndex = str.IndexOf("{$");
        if (strSIndex == -1) return str;
    }

    str = str.Substring(0, strSIndex) + str.Substring(strEIndex + 1);

    return Re(str);
}

Regex Method

Regex re = new Regex(@"\{(?:#|\$)(\w+)}", RegexOptions.Compiled);
re.Replace(str, "");

Results (few replaces):

Fn: IndexOf
Ticks: 1181967

Fn: Regex
Ticks: 1482261

Notice that regex was set to compile before the iterations.

Results (lots of replaces):

Fn: Regex
Ticks: 19136772

Fn: IndexOf
Ticks: 37457111