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?

How many different "something" value keys (the in the original string) so you have to deal with? The solution for "only one or two" possible values may be different from the one for "several dozen". — JaredReisinger, Oct 15 '10 at 23:45
possible duplicate of [Memory Efficiency and Performance of String.Replace .NET Framework](http://stackoverflow.com/questions/399798/memory-efficiency-and-performance-of-string-replace-net-framework) — Dour High Arch, Oct 16 '10 at 00:40

score 2 · Answer 1 · answered Oct 15 '10 at 21:43

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().

score 1 · Answer 2 · answered Oct 15 '10 at 21:49

1

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}

answered Oct 15 '10 at 21:49

tinifni

2,372
18
15

1

No problem. You might want to investigate Matt Brunell's answer though. Don't forget to accept an answer once you have found one that suits you. Happy coding! – tinifni Oct 15 '10 at 23:44

score 1 · Accepted Answer · answered Oct 16 '10 at 00:07

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

Regex from @tinifni's answer. – BrunoLM Oct 16 '10 at 00:08 — BrunoLM, Oct 16 '10 at 00:08

score 0 · Answer 4 · edited May 23 '17 at 09:58

0

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

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

edited May 23 '17 at 09:58

Community

1
1

answered Oct 15 '10 at 21:34

Dean Kuga

11,878
8
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This would be a two-pass algorithm: once for replacing `{#Text}` and another for replacing `{$Text}`. The OP explicitly requested a one-pass solution. – Kirk Woll Oct 15 '10 at 21:36
I don't think "is there a way to just do one compiled regex and do a single pass through?" qualifies as an explicit request for a one-pass solution... – Dean Kuga Oct 15 '10 at 21:40

score 0 · Answer 5 · answered Oct 15 '10 at 21:43

0

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.

answered Oct 15 '10 at 21:43

Yuriy

2,670
6
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Replace {#Text} and {$Text} in a string, in a performant way

SomethingBlahBlah can be #SomeThingOtherthanThis

5 Answers5