Get A Substring After Finding A Keyword In C#

Introduction

In C#, during string parsing is not always neatly come in a comma-separated format or the pattern is not based on a single character but on a word. User-generated system logs and different texts may have a pattern but it is based on certain keywords to signal when to get the information that is needed. Consider the following example.

User-Generated Log Example

System Services Start
System Services Start End
Service1 Start
Service1 Error Code:39322
System Service2 Start
Service1 Error Code:48340

Get Substring Using Span Slice After A Keyword Search

In this example, we get a list of different logs, however, we are interested in the error codes. If we just want to write a function that when we find the lines that have keyword text 'Error Code:' get the rest of the string by using a substring method so that we can get the numerical value. Later in our code, we could convert the numerical value to an int if need to.

Span Slice After A Keyword Search Code Example

string errorCodeLine = "Service1 Error Code:39322";//starting error code line
string newText = GetStringBasedOnKeyword("Error Code:",errorCodeLine);
Console.WriteLine(newText);
string GetStringBasedOnKeyword(string keyword, string textToParse)
{
    int keywordIndex = textToParse.LastIndexOf(keyword) + keyword.Length;//find the start of the keyword and to find the end need to add the length of the keyword 
    Span<char> textSpan = new Span<char>(textToParse.ToCharArray());//Convert text to a span for faster memory allocation
    Span<char> newText = textSpan.Slice(keywordIndex);//Get the rest of the string based on the start index of the keyword
    return newText.ToString();
}

Code Output

39322

As you can see this works to separate the number by using a keyword. This method uses span slice as it is the fastest way method to get the rest of the string.

Span Slice After A Keyword Search Speed Code Example

Since span slice is not using the heap and so avoids garbage collection, it is expected that this method would be fast. Let's see how it performs.

using System.Diagnostics;
int numberOfTests = 10;//Number of tests 
List<double> testSpeedList = new List<double>();
for (int i = 0; i < numberOfTests; i++)
{
    testSpeedList.Add(SliceSpeedTest());
}
Console.WriteLine($"Slice Average speed:{Math.Round(testSpeedList.Average())}ms, In {numberOfTests} tests");
double SliceSpeedTest()
{
    int numberOfFunctionCalls = 100000000;//Number of function calls made
    string errorCodeLine = "Service1 Error Code:39322";//starting error code line
    string keyword = "Error Code:";
    Stopwatch stopwatch = new Stopwatch();
    stopwatch.Start();//Start the Stopwatch timer
    string alteredText = "";
    for (int i = 0; i < numberOfFunctionCalls; i++)
    {
        alteredText = GetSliceBasedOnKeyword(keyword, errorCodeLine);//Function under test
    }
    stopwatch.Stop();//Stop the Stopwatch timer
    Console.WriteLine($"sampleText:{errorCodeLine}, alteredText:{alteredText}, Function calls:{numberOfFunctionCalls}, In {stopwatch.Elapsed.Minutes}m {stopwatch.Elapsed.Seconds}s {stopwatch.Elapsed.Milliseconds}ms");
    return stopwatch.Elapsed.TotalMilliseconds;
}
string GetSliceBasedOnKeyword(string keyword, ReadOnlySpan<char> newText)
{
    int keywordIndex = newText.LastIndexOf(keyword) + keyword.Length;//find start the keyword and to find the end need to add the length of the keyword 
    ReadOnlySpan<char> newText2 = newText.Slice(keywordIndex);//Convert text to a span for faster memory allocation
    return newText2.ToString();
}

Code Output

sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 4s 16ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 3s 767ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 3s 768ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 3s 758ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 3s 751ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 3s 777ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 3s 763ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 3s 750ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 3s 723ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 3s 724ms
Slice Average speed:3780ms, In 10 tests

How Concise Is The Code Using Span Slice?

We evaluate how concise it is by how many lines of code it takes for each step. In this case, 3 lines of code are good. One line to find the keyword and another to get the substring.

How Readable Is The Code Using Span Slice?

There are a couple of setup steps along with the new Span syntax and there is a background to understanding implementing the span but once that is done. It comes down to setting up and allocating memory then calling the Slice method which is fairly easy to understand.

Get Substring Using String Substring After Keyword Search

Here is an example of the same process but instead of using span slice the string substring method is used. This is still a viable approach but I have it second here because the performance is slower than span slice. Substring is easier to read because there is one less line for allocating memory. See the example below.

String Substring After Keyword Search Code Example

string errorCodeLine = "Service1 Error Code:39322";//starting error code line
string newText = GetSubstringBasedOnKeyword("Error Code:", errorCodeLine);
Console.WriteLine(newText);
string GetSubstringBasedOnKeyword(string keyword, string textToParse)
{
    int keywordIndex = textToParse.LastIndexOf(keyword) + keyword.Length;//find the start of the keyword and to find the end need to add the length of the keyword 
    string newText = textToParse.Substring(keywordIndex);//Get the rest of the string based on the start index of the keyword
    return newText;
}

Code Output

39322

As expected, the substring returns the same result as the slice.

String Substring After A Keyword Search Speed Code Example

using System.Diagnostics;
int numberOfTests = 10;//Number of tests 
List<double> testSpeedList = new List<double>();
for (int i = 0; i < numberOfTests; i++)
{
    testSpeedList.Add(SubstringSpeedTest());
}
Console.WriteLine($"Substring Average speed:{Math.Round(testSpeedList.Average())}ms, In {numberOfTests} tests");
double SubstringSpeedTest()
{
    int numberOfFunctionCalls = 100000000;//Number of function calls made
    string errorCodeLine = "Service1 Error Code:39322";//starting error code line
    string keyword = "Error Code:";
    Stopwatch stopwatch = new Stopwatch();
    stopwatch.Start();//Start the Stopwatch timer
    string alteredText = "";
    for (int i = 0; i < numberOfFunctionCalls; i++)
    {
        alteredText = GetSubstringBasedOnKeyword(keyword, errorCodeLine);//Function under test
    }
    stopwatch.Stop();//Stop the Stopwatch timer
    Console.WriteLine($"sampleText:{errorCodeLine}, alteredText:{alteredText}, Function calls:{numberOfFunctionCalls}, In {stopwatch.Elapsed.Minutes}m {stopwatch.Elapsed.Seconds}s {stopwatch.Elapsed.Milliseconds}ms");
    return stopwatch.Elapsed.TotalMilliseconds;
}
string GetSubstringBasedOnKeyword(string keyword, string textToParse)
{
    int keywordIndex = textToParse.LastIndexOf(keyword) + keyword.Length;//find the start of the keyword and to find the end need to add the length of the keyword 
    string newText = textToParse.Substring(keywordIndex);//Get the rest of the string based on the start index of the keyword
    return newText;
}

Code Output

sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 6s 771ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 6s 645ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 6s 624ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 6s 621ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 6s 610ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 6s 617ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 6s 618ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 6s 604ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 6s 611ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 6s 568ms
Substring Average speed:6629ms, In 10 tests

Although the substring is not slow it seems slow compared to span slice.

How Concise Is The Code Using String Substring?

The setup and function call of the substring takes only 3 lines of code which is compact.

How Readable Is The Code Using Span Slice?

Readable suffers a little since that is short and it doesn't describe what is happening that well. Probably would have to debug this to understand better what is happening.

Get Substring Using String Split After A Keyword Search

Using string split we can cut the string in half by the keyword. Then take the second half and immediately return to the substring. This is the most compact way to solve this problem but it does suffer from readability as it would not be as clear from reading the code what is happening without an example. See the code below.

String Split On Keyword Code Example

string errorCodeLine = "Service1 Error Code:39322";//starting error code line
string newText = GetSplitBasedOnKeyword("Error Code:", errorCodeLine);
Console.WriteLine(newText);
string GetSplitBasedOnKeyword(string keyword, string textToParse)
{
    string[] cutText = textToParse.Split(keyword);//find start the keyword and to find the end need to add the length of the keyword 
    return cutText[1];//return the second half the string which will be the error code
}

Code Output

39322

Get Substring Using String Split After A Keyword Search

Based on how many lines of code we might expect to find that split would be fast but let's test to see how fast it is.

String Substring After A Keyword Search Code Example

using System.Diagnostics;
int numberOfTests = 10;//Number of tests 
List<double> testSpeedList = new List<double>();
for (int i = 0; i < numberOfTests; i++)
{
    testSpeedList.Add(SplitSpeedTest());
}
Console.WriteLine($"Split Average speed:{Math.Round(testSpeedList.Average())}ms, In {numberOfTests} tests");
double SplitSpeedTest()
{
    int numberOfFunctionCalls = 100000000;//Number of function calls made
    string errorCodeLine = "Service1 Error Code:39322";//starting error code line
    string keyword = "Error Code:";
    Stopwatch stopwatch = new Stopwatch();
    stopwatch.Start();//Start the Stopwatch timer
    string alteredText = "";
    for (int i = 0; i < numberOfFunctionCalls; i++)
    {
        alteredText = GetSplitBasedOnKeyword(keyword, errorCodeLine);//Function under test
    }
    stopwatch.Stop();//Stop the Stopwatch timer
    Console.WriteLine($"sampleText:{errorCodeLine}, alteredText:{alteredText}, Function calls:{numberOfFunctionCalls}, In {stopwatch.Elapsed.Minutes}m {stopwatch.Elapsed.Seconds}s {stopwatch.Elapsed.Milliseconds}ms");
    return stopwatch.Elapsed.TotalMilliseconds;
}
string GetSplitBasedOnKeyword(string keyword, string textToParse)
{
    string[] cutText = textToParse.Split(keyword);//find start the keyword and to find the end need to add the length of the keyword 
    return cutText[1];//return the second half of the string which will be the error code
}

Code Output

sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 5s 212ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 4s 810ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 4s 779ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 4s 791ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 4s 744ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 4s 749ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 4s 775ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 4s 749ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 4s 780ms
sampleText:Service1 Error Code:39322, alteredText:39322, Function calls:100000000, In 0m 4s 756ms
Split Average speed:4815ms, In 10 tests

We see how that split is faster than substring but not as fast as a slice. It has good speed.

How Concise Is The Code Using Span Slice?

This is pretty compact at only 2 lines so this means less typing.

How Readable Is The Code Using Span Slice?

Readable suffers a little since that is short and it doesn't really describe what is happening that well. Probably would have to debug this to understand better what is happening.

Conclusion

The overall best way to solve this problem statement is with Span Slice because of the huge performance gain and we weigh the performance so much because that would most impact the customer. Also, while slice may not be as readable and concise as the other two methods it still isn't that bad. Concise and readability are more productivity metrics for the developer and they are important to the developmental process. If another developer has a harder time reading your code then impacts the productivity of the whole team. While having fewer lines of code that do the same improves productivity and you get more done.