Using LastIndexOf and Substring with an array

Question

Basically I'm reading in 50 lines from a text file which has a format somewhat like this for each line:

David Chalmers 34

I've read the text file using ReadAllLines so each line should be a different entry in the array.

I'm trying to take the number from each line and store them into an array of their own. Right now I'm getting the error:

Index and length must refer to a location within the string.

static void getResults(string[] Text)
{
    // X = lastIndexOf for ' ' (space)
    // x will take position of the last space
    // Results = substring
    // z will be the length of the string
    // z = text.Length
    //  Substring (x+1,z-x+1)

    int lines = 50;
    string[] Results = new string[lines];
    for (int i = 0; i < Text.Length; i++)
    {
        int x = Text[i].LastIndexOf(' ');
        int z = Text[i].Length;

        Results[lines] = Text[i].Substring(x + 1, z - x + 1);
    }
}

Any help would be appreciated!

Did you use the debugger and check your variables when you get this error? — Soner Gönül
– Soner Gönül, Commented Dec 17, 2015 at 15:23
Results[50] will be off the array - presumably you want Results[i] — StuartLC
– StuartLC, Commented Dec 17, 2015 at 15:25
Do you realize that you are writing always at the same position in the array (lines=50)? And that position doesn't exist because arrays in NET start at zero and ends at length - 1 (max 49 here)? — Steve
– Steve, Commented Dec 17, 2015 at 15:25
I am not sure why you don't use the string.Split() method to do this it would be more efficient and less code also what if you get more than 50 lines.. at least the Split function would still work as long as the file format remains the same.. — MethodMan
– MethodMan, Commented Dec 17, 2015 at 15:28

Steve Wellens · Accepted Answer · 2015-12-17 15:26:29Z

4

Use Split, it's a lot easier:

String Test = "David Chalmers 34";

String[] Segments = Test.Split(' ');

Console.WriteLine(Segments[2]);

Console.ReadKey();

Of course, you'll want to add error handling for bad input.

answered Dec 17, 2015 at 15:26

Steve Wellens

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Comments

Albireo · Accepted Answer · 2015-12-17 15:25:04Z

1

You must subtract 1 from the substring length instead of adding it:

var line = "David Chalmers 34";
var lineLength = line.Length; // == 17
var lastSpacePosition = line.LastIndexOf(' '); // == 14
var age = line.Substring(lastSpacePosition + 1, lineLength - lastSpacePosition - 1); // == 34

answered Dec 17, 2015 at 15:25

Albireo

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Comments

Dusan · Accepted Answer · 2015-12-17 15:25:42Z

1

Your expression should be:

Results[lines] = Text[i].Substring(x + 1, z - x - 1);

You need to substract 1 instead of adding.

answered Dec 17, 2015 at 15:25

Dusan

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Comments

StuartLC · Accepted Answer · 2015-12-17 15:29:08Z

0

You can also do all of this in one line of Linq:

var Results = Text.Take(50)
    .Select(line => line.Split(' '))
    .Select(sa => sa.Last())
    .ToArray();

answered Dec 17, 2015 at 15:29

StuartLC

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Comments

rory.ap · Accepted Answer · 2015-12-17 15:42:59Z

Here's what I would do, making use of a Person class. It may not seem necessary right now given the scope of your project, but if the scope ever grows, using classes and instances will pay off. Plus, this way, you have the names to match the ages you're seeking which is probably going to be necessary at some point anyway.

public static List<Person> GetResults(string[] text)
{
    var results = new List<Person>();

    foreach(var line in text)
    {
        results.Add(Person.Parse(line));
    }

    return results;
}

public class Person
{
    public string Name { get; private set; }
    public int Age { get; private set; }

    public Person(string name, int age)
    {
        Name = name;
        Age = age;
    }

    public static Person Parse(string fromInputLine)
    {
        ValidateInput(fromInputLine);
        var delimPosition = fromInputLine.LastIndexOf(' ');
        var name = fromInputLine.Substring(0, delimPosition);
        var age = Convert.ToInt32(fromInputLine.Substring(delimPosition + 1));
        return new Person(name, age);
    }

    private static void ValidateInput(string toValidate)
    {
        if (!System.Text.RegularExpressions.Regex.IsMatch(toValidate, @"^.+\s+\d+$")) 
            throw new ArgumentException(string.Format(@"The provided input ""{0}"" is not valid.", toValidate));
    }
}

Jack1987 · Accepted Answer · 2015-12-17 15:54:44Z

0

You can use the method .Split from string class, what he does is to separate the string by the blank spaces, then you get an array of strings...

var entry = "David Chambers 34";
string[] result = entry.Split(" ")

then you can convert to integer

var age = Convert.ToInt32(result[2]);

or

var age = Int32.TryParse(result[2]);

answered Dec 17, 2015 at 15:54

Jack1987

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Comments

TVOHM · Accepted Answer · 2015-12-17 15:54:46Z

0

To store the numbers in an array of their own, you could try:

string[] numbers = text.Select(x => x.Substring(x.LastIndexOf(' '))).ToArray();

answered Dec 17, 2015 at 15:54

TVOHM

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Comments

jdweng · Accepted Answer · 2015-12-17 15:29:23Z

-1

Use a StringReader

        static void getResults(string Text)
        {

            // X = lastIndexOf for ' ' (space)
            // x will take position of the last space
            // Results = substring
            // z will be the length of the string
            // z = text.Length
            //  Substring (x+1,z-x+1)

            StringReader reader = new StringReader(Text);

            List<string> Results = new List<string>();
            string inputLine = "";
            while ((inputLine = reader.ReadLine()) != null)
            {
                Results.Add(inputLine.Trim());
            }
        }

answered Dec 17, 2015 at 15:29

jdweng

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4 Comments

Albireo Over a year ago

This doesn't do what OP is asking for (getting only the number).

jdweng Over a year ago

Yes it does : "the number from each line and store them into an array of their own". The person didn't say to parse the number to a integer.

Albireo Over a year ago

You're returning the whole line, not only the number part as asked: Results.Add(inputLine.Trim()); (and your method parameter is wrong too, should be string[] not string).

jdweng Over a year ago

I think the string[] is wrong. Getting an array would convert to an array of characters and not an array of strings.

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