How do I extract a substring from a string until the second space is encountered?

I have a string like this:

"o1 1232.5467 1232.5467 1232.5467 1232.5467 1232.5467 1232.5467"

How do I extract only "o1 1232.5467"?

The number of characters to be extracted are not the same always. Hence, I want to only extract until the second space is encountered.

A straightforward approach would be the following:

string[] tokens = str.Split(' ');
string retVal = tokens[0] + " " + tokens[1];

Just use String.IndexOf twice as in:

     string str = "My Test String";
     int index = str.IndexOf(' ');
     index = str.IndexOf(' ', index + 1);
     string result = str.Substring(0, index);

Get the position of the first space:

int space1 = theString.IndexOf(' ');

The the position of the next space after that:

int space2 = theString.IndexOf(' ', space1 + 1);

Get the part of the string up to the second space:

string firstPart = theString.Substring(0, space2);

The above code put togehter into a one-liner:

string firstPart = theString.Substring(0, theString.IndexOf(' ', theString.IndexOf(' ') + 1));

s.Substring(0, s.IndexOf(" ", s.IndexOf(" ") + 1))

Use a regex: .

Match m = Regex.Match(text, @"(.+? .+?) ");
if (m.Success) {
    do_something_with(m.Groups[1].Value);
}

Something like this:

int i = str.IndexOf(' ');
i = str.IndexOf(' ', i + 1);
return str.Substring(i);

string testString = "o1 1232.5467 1232.5467.........";

string secondItem = testString.Split(new char[]{' '}, 3)[1];

😛

Just a note, I think that most of the algorithms here wont check if you have 2 or more spaces together, so it might get a space as the second word.

I don’t know if it the best way, but I had a little fun linqing it 😛 (the good thing is that it let you choose the number of spaces/words you want to take)

        var text = "a sdasdf ad  a";
        int numSpaces = 2;
        var result = text.TakeWhile(c =>
            {
                if (c==' ')
                    numSpaces--;

                if (numSpaces <= 0)
                    return false;

                return true;
            });
        text = new string(result.ToArray());

I also got @ho’s answer and made it into a cycle so you could again use it for as many words as you want 😛

        string str = "My Test String hello world";
        int numberOfSpaces = 3;
        int index = str.IndexOf(' ');     

        while (--numberOfSpaces>0)
        {
            index = str.IndexOf(' ', index + 1);
        }

        string result = str.Substring(0, index);

 string[] parts = myString.Split(" ");
 string whatIWant = parts[0] + " "+ parts[1];

There are shorter ways of doing it like others have said, but you can also check each character until you encounter a second space yourself, then return the corresponding substring.

static string Extract(string str)
{
    bool end = false;
    int length = 0 ;
    foreach (char c in str)
    {
        if (c == ' ' && end == false)
        {
            end = true;
        }
        else if (c == ' ' && end == true)
        {
            break;
        }

        length++;
    }

    return str.Substring(0, length);
}

I would recommend a regular expression for this since it handles cases that you might not have considered.

var input = "o1 1232.5467 1232.5467 1232.5467 1232.5467 1232.5467 1232.5467";
var regex = new Regex(@"^(.*? .*?) ");
var match = regex.Match(input);
if (match.Success)
{
    Console.WriteLine(string.Format("'{0}'", match.Groups[1].Value));
}

I was thinking about this problem for my own code and even though I probably will end up using something simpler/faster, here’s another Linq solution that’s similar to one that @Francisco added.

I just like it because it reads the most like what you actually want to do: “Take chars while the resulting substring has fewer than 2 spaces.”

string input = "o1 1232.5467 1232.5467 1232.5467 1232.5467 1232.5467 1232.5467";
var substring = input.TakeWhile((c0, index) => 
                                input.Substring(0, index + 1).Count(c => c == ' ') < 2);
string result = new String(substring.ToArray());

I did some benchmarks for some solutions in this post and got these results (if performance is important):

Fastest Method (answer from @Hans Olsson):

string str = "My Test String";
int index = str.IndexOf(' ');
index = str.IndexOf(' ', index + 1);
string result = str.Substring(0, index);

@Guffa added a one-liner for this solution (and explained bit by bit of what’s going on), which I personally prefer.

Methods checked:

public string Method1(string str)
{
    string[] tokens = str.Split(' ');
    return tokens[0] + " " + tokens[1];
}

public string Method2(string str)
{
    int index = str.IndexOf(' ');
    index = str.IndexOf(' ', index + 1);
    return str.Substring(0, index);
}

public string Method3(string str)
{
    Match m = Regex.Match(str, @"(.+? .+?) ");
    if (m.Success)
    {
        return m.Groups[1].Value;
    }

    return string.Empty;
}

public string Method4(string str)
{
    var regex = new Regex(@"^(.*? .*?) ");
    Match m = regex.Match(str);
    if (m.Success)
    {
        return m.Groups[1].Value;
    }

    return string.Empty;
}

public string Method5(string str)
{
    var substring = str.TakeWhile((c0, index) =>
                        str.Substring(0, index + 1).Count(c => c == ' ') < 2);
    return new String(substring.ToArray());
}

Method execution times with 100000 runs

using OP’s input:

string value = "o1 1232.5467 1232.5467 1232.5467 1232.5467 1232.5467 1232.5467";

Method1 took 38ms (00:00:00.0387240)
Method2 took 5ms (00:00:00.0051046)
Method3 took 100ms (00:00:00.1002327)
Method4 took 393ms (00:00:00.3938484)
Method5 took 147ms (00:00:00.1476564)

using a slightly longer input (spaces far into the string):

string value = "o11232.54671232.54671232.54671232.54671232.54671232.5467o11232.54671232.54671232.54671232.54671232.54671232.5467o1 1232.5467 1232.5467 1232.5467 1232.5467 1232.5467 1232.5467";

Method1 took 71ms (00:00:00.0718639)
Method2 took 20ms (00:00:00.0204291)
Method3 took 282ms (00:00:00.2822633)
Method4 took 541ms (00:00:00.5416347)
Method5 took 5335ms (00:00:05.3357977)