CODEWITHSUNDEEP
c#
Greg
Greg

Reputation: 13

Cleanest way to truncate last items in a comma delimited string?

What is the best/cleanest way you know of to take a comma delimited string, such as "A,B,C,D,E,F,G", and return only the 1st x amount of items in the list? So if x = 5 then the result would be "A,B,C,D,E".

I know there are different ways to do this: "for loop" counting commas, then truncate string; split string to array or list, then remove last x amount of items.

Is there a cleaner, more efficient option that I don't know of? How would you go about this?

Thanks in advance!! Greg

Upvotes: 0

Views: 2029

Answers (7)

djs
djs

Reputation: 230

This should work if you want to do it with just String methods (not Take()):

string.Join(",", s.Split(","), 0, 5);

If you know each element is only one character, you can do:

s.Substring(0, 2*x - 1);

Upvotes: 0

Jon Egerton
Jon Egerton

Reputation: 41549

Just for fun - using Regex/String methods only (I wouldn't use Regex to do this real world - then I'd have two problems):

string.SubString(0,Regex.Matches(string,",")[x-1].Index);

Upvotes: 0

Jon Skeet
Jon Skeet

Reputation: 1500495

I would split the task into two parts:

  • Splitting the string by commas
  • Taking only the first N values

Fortunately C# makes both of these pretty simple, with String.Split handling the first, and the LINQ Take method handling the second:

var items = text.Split(',')
                .Take(itemLimit);

Or if you want to create a list:

var items = text.Split(',')
                .Take(itemLimit)
                .ToList();

I would not convert it back into a comma-delimited string unless you really need to. Keep the most natural representation of the data (e.g. a List<string>) for as long as you can. If you need to, just use String.Join.

You could potentially make the Split part more efficient by writing a "lazy splitter" - but it would be work for very little gain, IMO, unless you expect to get a very long string and only want to keep a few items. It would look something like this:

public static IEnumerable<string> LazySplit(this string text, string separator)
{
    int start = 0;
    while (true)
    {
        int end = text.IndexOf(separator, start);
        if (end == -1)
        {
            // Note: if the string ends with the separator, this will yield
            // an empty string
            yield return text.Substring(start);
            yield break; // This will terminate the otherwise-infinite loop
        }
        yield return text.Substring(start, end - start);
        start = end + separator.Length;
    }
}

Then the usage code is similar to before:

var items = text.LazySplit(",")
                .Take(itemLimit)
                .ToList();

Alternatively, if you really, really need to keep it in a string, you could just write something to find the Nth comma, and just use Substring to take the first part of the string:

// TODO: Improve the name :)
public static string TruncateAfterSeparatorCount(string text,
                                                 string separator,
                                                 int count)
{
    // We pretend that the string "starts" with a separator before index 0.
    int index = -separator.Length;
    for (int i = 0; i < count; i++)
    {
        int nextIndex = text.IndexOf(separator, index + separator.Length);
        // Not enough separators. Return the whole string. Could throw instead.
        if (nextIndex == -1)
        {
            return text;
        }
        index = nextIndex;
    }
    // We need to handle the count == 0 case, where index will be negative...
    return text.Substring(0, Math.Max(index, 0));
}

But as I say, I would personally try to use the List<string> approach if possible. The above code is clearly significantly more complex than Split/Take/ToList, even though it's more efficient. Only use more efficient but more complicated code when you've proved there's a need.

Upvotes: 5

Mathew Thompson
Mathew Thompson

Reputation: 56429

Probably a Split and a Take.

Try this:

string yourString = "A,B,C,D,E,F,G";
List<string> items = yourString.Split(',')
    .Take(5)
    .ToList();
string output = string.Join(",", items);

Upvotes: 0

Michael Ross
Michael Ross

Reputation: 570

    string[] List = SubList(5);
    string Output = string.Join(",", List);

private string[] SubList(int p)
{
    string[] List = new string[] { "A", "B", "C", "D", "E", "F" };
    string[] List2 = new string[p];
    for (int i = 0; i < p; i++)
        List2[i] = List[i];
    return List2;
}

Upvotes: 0

COLD TOLD
COLD TOLD

Reputation: 13579

string[] words = s.Split(',').Take(5);

Upvotes: 0

alex
alex

Reputation: 12654

Try this:

string.Join("," , str.Split(",").Take(5));

Or, if you do it regularly, you can write an extension method just for that.

Upvotes: 3

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