How to concat various chunks of string array based on a condition

Question

Lets say i have a string array like this,

string[] array1 = { 
    "<p>here is a big sentence</p>",
    "file1",
    "file2",
    "<p>this is a big paragraph</p>",
    "file3",
    "file4",
    "file5",
    "<p>this is another paragraph</p>",
    };

i want to convert this to,

string[] array2 = { 
    "<p>here is a big sentence</p>",
    "file1,file2",
    "<p>this is a big paragraph</p>",
    "file3,file4,file5",
    "<p>this is another paragraph</p>",
    };

i need to concat strings, inside an array, based on a condition, that they don't have a <p></p> tag.

what is cleanest way to do this, is there a correct way to do this? with or without linq?

Answer 1

A somewhat general solution would be to write a GroupStrings() method which groups the strings into arrays according to a supplied predicate:

public static IEnumerable<string[]> GroupStrings(IEnumerable<string> strings, Predicate<string> shouldBeGrouped)
{
    var group = new List<string>();

    foreach (var s in strings)
    {
        if (shouldBeGrouped(s))
        {
            group.Add(s);
        }
        else
        {
            if (group.Count > 0)
            {
                yield return group.ToArray();
                group.Clear();
            }

            yield return [s];
        }
    }

    if (group.Count > 0)
    {
        yield return group.ToArray();
    }
}

Then you can create the required resulting array by calling that as follows:

var groups = GroupStrings(array1, s => !s.StartsWith("<p>") || !s.EndsWith("</p>"));
var array2 = groups.Select(group => string.Join(",", group));

Answer 2

Iterator blocks are often useful when you want to write some more complicated LINQ-type functionality. Something like this for example:

public static IEnumerable<string> MyIteratorBlockMethod(IEnumerable<string> source)
{
    var sb = new StringBuilder();
    foreach (var s in source)
    {
        if (s.Contains("<p>")) // or whatever condition you want
        {
            if (sb.Length > 0)
            {
                yield return sb.ToString();
                sb.Clear();
            }

            yield return s;
        }
        else
        {
            if (sb.Length > 0)
            {
                sb.Append(',');
            }

            sb.Append(s);
        }
        
    }
   if (sb.Length > 0){
      yield return sb.ToString();
   }
}

Use like

[Test]
public void MergeTest()
{
    string[] array1 = {
        "<p>here is a big sentence</p>",
        "file1",
        "file2",
        "<p>this is a big paragraph</p>",
        "file3",
        "file4",
        "file5",
        "<p>this is another paragraph</p>",
    };
    var result = MyIteratorBlockMethod(array1).ToArray();
}

Answer 3

I'd perhaps use a List<string> with a StringBuilder like this:

string[] array1 = {
    "<p>here is a big sentence</p>",
    "file1",
    "file2",
    "<p>this is a big paragraph</p>",
    "file3",
    "file4",
    "file5",
    "<p>this is another paragraph</p>",
};

var result = new List<string>(array1.Length);
var builder = new StringBuilder();

foreach (var row in array1)
{
    if (row.StartsWith("<p>", StringComparison.Ordinal) && row.EndsWith("</p>", StringComparison.Ordinal))
    {
        // if we already have data collected, we should add this before
        // adding the next <p></p> row
        if (builder.Length > 0)
        {
            result.Add(builder.ToString());
            builder.Clear();
        }

        // add the <p></p> row
        result.Add(row);
        // proceed to the next item in array1
        continue;
    }

    // Add commas as necessary
    if (builder.Length > 0)
    {
        builder.Append(',');
    }
    // add the row data
    builder.Append(row);
}

// We could end up here with in situations where the last item isn't <p></p>, so we'll add the last item if necessary
if (builder.Length > 0)
{
    result.Add(builder.ToString());
}

Answer 4

string[] array1 = {
    "<p>here is a big sentence</p>",
    "file1",
    "file2",
    "<p>this is a big paragraph</p>",
    "file3",
    "file4",
    "file5",
    "<p>this is another paragraph</p>",
};

List<string> result = new List<string>();

// Temporary list to hold the files between <p> tags
List<string> tempFiles = new List<string>();

foreach (var item in array1)
{
    if (item.StartsWith("<p>"))
    {
        // If there are files in tempFiles, concatenate them and add to result
        if (tempFiles.Any())
        {
            result.Add(string.Join(",", tempFiles));
            tempFiles.Clear(); // Clear the tempFiles list for next batch
        }
        // Add the <p> tag item to the result
        result.Add(item);
    }
    else
    {
        // Collect files between <p> tags
        tempFiles.Add(item);
    }
}

// If there are any remaining files in tempFiles, add them to result
if (tempFiles.Any())
{
    result.Add(string.Join(",", tempFiles));
}

// Convert result list to array
string[] array2 = result.ToArray();

foreach (var str in array2)
{
    Console.WriteLine(str);
}