C#•2y ago

Get multiple substrings from a main string

I feel like this should be basic knowledge, but whatever, imma ask anyways.. Say I have a string base insert some esab weird strings base here esab and I wanted to get every bit that is between two other strings, in this case base as "start" and esab as "end" So I would want to get every substring between start, and end. Beneath is what I expect to happen with the code.

string input = "base insert some esab weird strings base here esab";
string start = "base";
string end = "esab";

string result = [ "insert some", "here" ];

string input = "base insert some esab weird strings base here esab";
string start = "base";
string end = "esab";

string result = [ "insert some", "here" ];

I feel I should probably be using input.Substring(input.IndexOf(start), input.IndexOf(end) + end.Length) or something, but it's missing something and I can't see it.

57 Replies

Pobiega•2y ago

it needs a loop and some offset from the previous iteration dont forget that substring takes startIndex, length, not startIndex, stopIndex

malkav•2y ago

and how would I do that? something like:

string[] result = Array.Empty<string>();
do
{
  int starting = input.IndexOf(start) + start.Length;
  result[result.Length] = input.SubString(starting, input.IndexOf(end) - starting);
} while (!input.IsNullOrEmpty)

string[] result = Array.Empty<string>();
do
{
  int starting = input.IndexOf(start) + start.Length;
  result[result.Length] = input.SubString(starting, input.IndexOf(end) - starting);
} while (!input.IsNullOrEmpty)

(I don't think I did the loop right, but you get the gist right?)

Pobiega•2y ago

yeah you're really close you'll need a list instead of an array thou, because you dont know the size

malkav•2y ago

Ah fair. (this is why I did result.Length but I guess a List would be easier)

Pobiega•2y ago

you also need an exit condition :p

malkav•2y ago

what would be my exit condition though, because rn I don't think my input will ever reach nullOrEmpty 😅

Pobiega•2y ago

you are not changing your input hint: what does .IndexOf return if it doesnt find anything?

malkav•2y ago

-1 right?

Pobiega•2y ago

correct

malkav•2y ago

so eh, do { stuff } while (input.IndexOf(start) + 1 != 0)? wait, no... hang on 😅 I got to think with this now..

Pobiega•2y ago

I started with something very similar, but refactored it into a while(true)

malkav•2y ago

because my IndexOf will never return -1 because I don't modify the input at all

Pobiega•2y ago

thats why you need the offset

malkav•2y ago

yea I have this now:

do
{
  int start = mainString.IndexOf(startString, StringComparison.Ordinal) + startString.Length;    
  results.Add(mainString.Substring(start, mainString.IndexOf(endString, StringComparison.Ordinal) - start));
} while (true);

do
{
  int start = mainString.IndexOf(startString, StringComparison.Ordinal) + startString.Length;    
  results.Add(mainString.Substring(start, mainString.IndexOf(endString, StringComparison.Ordinal) - start));
} while (true);

but I am missing the offset how do I offset

Pobiega•2y ago

should I post my solution? or do you wanna figure it out

malkav•2y ago

I wanna figure it out, but I would like help in guiding my thoughts to the solution if you don't mind? I learn more that way than pre-made code 😅

Pobiega•2y ago

ok so you need an offset for your indexOf so you dont find the same match forever this offset needs to live outside the loop obviously

Unknown User•2y ago

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Pobiega•2y ago

not sure how that helps, that part is already figured out

malkav•2y ago

hrm...

List<string> results = new();
int offset = 0;
do 
{
  int start = mainString.IndexOf(startString + offset) + startString.Length
  results.Add(mainString.Substring(start, mainString.IndexOf(endString + offset) - start);
  offset = offset + (prolly the Length of the startString + subString + endString??);
} while (offset != // I'm having a mind-stop here)

List<string> results = new();
int offset = 0;
do 
{
  int start = mainString.IndexOf(startString + offset) + startString.Length
  results.Add(mainString.Substring(start, mainString.IndexOf(endString + offset) - start);
  offset = offset + (prolly the Length of the startString + subString + endString??);
} while (offset != // I'm having a mind-stop here)

Pobiega•2y ago

😄

Unknown User•2y ago

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Pobiega•2y ago

you are SOOO close to my pre-refactor solution well lets just not introduce regexes

malkav•2y ago

I deliberately didn't choose for regex, because there are some prerequisites to this that cannot be done with Regex I know regex enough to do some things, but this is off topic 😅

Unknown User•2y ago

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malkav•2y ago

What am I missing for my offset let me re-iterate: "I cannot do that with regex" 🤣

Pobiega•2y ago

offset > -1 but this is where I refactored because I realized I had to set offset to a special value to signal the end and at that point, it was cleaner to use a while(true)

malkav•2y ago

yea and I need to change it constantly in the loop

Pobiega•2y ago

yeah but thats fine you just set it to indexof end

malkav•2y ago

but doesn't it find the same "iteration" of the end string? example: Some string here Another string here now if I set offset to mainString.IndexOf(endString) does it not set it to the very first every time?

Pobiega•2y ago

tbh I didnt set up unittests and try on a whole bunch of strings I just ran on your first prompt

malkav•2y ago

okay, lemme make a unit test for this one it seems I should turn the do/while around. Because it sets itself to -1 and then does another loop??

System.ArgumentOutOfRangeException : Length cannot be less than zero. (Parameter 'length')
   at System.String.Substring(Int32 startIndex, Int32 length)

System.ArgumentOutOfRangeException : Length cannot be less than zero. (Parameter 'length')
   at System.String.Substring(Int32 startIndex, Int32 length)

at this code:

[Test]
    public void StringHasSingleSubstring()
    {
        // Arrange
        const string testString = "<sub>Need this</sub>";
        const string startString = "<sub>";
        const string endString = "</sub>";
        
        // Act:
        List<string> results = new();
        
        int offset = 0;
        do
        {
            int start = testString.IndexOf(startString + offset, StringComparison.Ordinal) + startString.Length;    
            results.Add(testString.Substring(start, testString.IndexOf(endString + offset, StringComparison.Ordinal) - start));
            offset = testString.IndexOf(endString, StringComparison.Ordinal);
        } while (offset > -1);
        
        // Assert
        results.Count.Should().Be(1);
    }

[Test]
    public void StringHasSingleSubstring()
    {
        // Arrange
        const string testString = "<sub>Need this</sub>";
        const string startString = "<sub>";
        const string endString = "</sub>";
        
        // Act:
        List<string> results = new();
        
        int offset = 0;
        do
        {
            int start = testString.IndexOf(startString + offset, StringComparison.Ordinal) + startString.Length;    
            results.Add(testString.Substring(start, testString.IndexOf(endString + offset, StringComparison.Ordinal) - start));
            offset = testString.IndexOf(endString, StringComparison.Ordinal);
        } while (offset > -1);
        
        // Assert
        results.Count.Should().Be(1);
    }

Pobiega•2y ago

[Fact]
public void GetBetween_works_2()
{
    var output = "<sub>Some string here</sub> <sub>Another string here</sub>".GetBetween("<sub>", "</sub>");

    output.ShouldBeEquivalentTo(new[] { "Some string here", "Another string here" });
}

[Fact]
public void GetBetween_works_2()
{
    var output = "<sub>Some string here</sub> <sub>Another string here</sub>".GetBetween("<sub>", "</sub>");

    output.ShouldBeEquivalentTo(new[] { "Some string here", "Another string here" });
}

passes 🙂 GetBetween is my function (I made it an extension method)

malkav•2y ago

okay, can I see your extension method then?

Pobiega•2y ago

that would be my entire solution. you sure about it?

malkav•2y ago

yea, then I can see what I missed

Pobiega•2y ago

public static string[] GetBetween(this string input, string start, string end)
{
    var offset = 0;
    var results = new List<string>();

    while (true)
    {
        var startIndex = input.IndexOf(start, offset);
        var endIndex = input.IndexOf(end, offset);

        if (startIndex == -1 || endIndex == -1) return results.ToArray();
        results.Add(input.Substring(startIndex + start.Length, endIndex - startIndex - start.Length).Trim());
        offset = endIndex + 1;
    }
}

public static string[] GetBetween(this string input, string start, string end)
{
    var offset = 0;
    var results = new List<string>();

    while (true)
    {
        var startIndex = input.IndexOf(start, offset);
        var endIndex = input.IndexOf(end, offset);

        if (startIndex == -1 || endIndex == -1) return results.ToArray();
        results.Add(input.Substring(startIndex + start.Length, endIndex - startIndex - start.Length).Trim());
        offset = endIndex + 1;
    }
}

malkav•2y ago

Ah, you did while(true) where I did do{}while() 😅

Pobiega•2y ago

yup, and the offset needs to be added to the correct place 😛

malkav•2y ago

yea I didn't

Pobiega•2y ago

malkav•2y ago

Right,

I'm dumbdumb 🤣 but I see what I did wrong now Wait, why did you set the offset to endIndex + 1?

Pobiega•2y ago

because I did 😄 otherwise it errors out on length because the index will be greater than the string length, if the end is the very last thing

malkav•2y ago

Guess that works

malkav•2y ago

// Each of my tests look like this:
public void StringhasSingleSubstring()
{
  // Arrange: Here I set startstring to either of the following two values:
  const string testString = "<sub>Need this</sub>";
  // const string testString = "<sub>Need this</sub> <sub>And this</sub> <sub>and maybe this too?</sub>";
  const string startString = "<sub>"; // on the "IsMissing" functions, I set this to <subs> or the endstring to </subs>
  const string endString = "</sub>";
  // Act:
  string[] results = testString.GetBetween(startString,endString);
  
  // Assert:
  results.Should().Be(value); 
// Value is 1 for StringHasSingleSubstring(), 3 for StringHasMultipleSubstrings(), and 0 for both EndStringIsMissing_ReturnsEmptyArray() and StartStringIsMissing_ReturnsEmptyArray()
}

// Each of my tests look like this:
public void StringhasSingleSubstring()
{
  // Arrange: Here I set startstring to either of the following two values:
  const string testString = "<sub>Need this</sub>";
  // const string testString = "<sub>Need this</sub> <sub>And this</sub> <sub>and maybe this too?</sub>";
  const string startString = "<sub>"; // on the "IsMissing" functions, I set this to <subs> or the endstring to </subs>
  const string endString = "</sub>";
  // Act:
  string[] results = testString.GetBetween(startString,endString);
  
  // Assert:
  results.Should().Be(value); 
// Value is 1 for StringHasSingleSubstring(), 3 for StringHasMultipleSubstrings(), and 0 for both EndStringIsMissing_ReturnsEmptyArray() and StartStringIsMissing_ReturnsEmptyArray()
}

Pobiega•2y ago

[Fact]
public void GetBetween_works_1()
{
    var output = "base insert some esab weird strings base here esab".GetBetween("base", "esab");

    output.ShouldBeEquivalentTo(new[] { "insert some", "here" });
}

[Fact]
public void GetBetween_works_2()
{
    var output = "<sub>Some string here</sub> <sub>Another string here</sub>".GetBetween("<sub>", "</sub>");

    output.ShouldBeEquivalentTo(new[] { "Some string here", "Another string here" });
}

[Fact]
public void GetBetween_works_1()
{
    var output = "base insert some esab weird strings base here esab".GetBetween("base", "esab");

    output.ShouldBeEquivalentTo(new[] { "insert some", "here" });
}

[Fact]
public void GetBetween_works_2()
{
    var output = "<sub>Some string here</sub> <sub>Another string here</sub>".GetBetween("<sub>", "</sub>");

    output.ShouldBeEquivalentTo(new[] { "Some string here", "Another string here" });
}

these are the tests I used 🙂 using Shouldly for the asserts

malkav•2y ago

I'm using FluentAssertions 😅 but then again, I use nUnit instead of xUnit

Pobiega•2y ago

yeah I love that one its what I use for more serious projects

malkav•2y ago

Heck yes. Plus I get smacks from the senior here if I don't test for failed cases too 🤣 hence the "Is Missing" tests

Pobiega•2y ago

sure

malkav•2y ago

I can't however test my Azure Function (or don't know how) the same way

Pobiega•2y ago

lets just say, I didn't bother writing production quality tests for this 😄

malkav•2y ago

hahaha no I recon, though I might have to, so I'll spend the next 45 minutes of the Hackaton here to work out how to Unit Test on Azure Functions thanks for your help man! much appreciated

Pobiega•2y ago

hm? you just test the actual functionality locally oh you code directly ON the azure function? eugh

malkav•2y ago

No I do it in Rider.

Pobiega•2y ago

riiight then just run the tests locally on rider too?

malkav•2y ago

for some reason, I can't even run the azure function in the debugger, and if I call the Azure Function from my nUnit Tests, then I need to pass the parameters that Azure Functions require, which I cannot instantiate from nowhere...

public static async Task<IActionResult> RunAsync(
        [HttpTrigger(AuthorizationLevel.Function, "post", Route = null)]
        HttpRequest req, ILogger log)
    {

public static async Task<IActionResult> RunAsync(
        [HttpTrigger(AuthorizationLevel.Function, "post", Route = null)]
        HttpRequest req, ILogger log)
    {

those parameters anyways, brb. I finally have 5 minutes for a smoke lol

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Get multiple substrings from a main string