How to skip first line while reading csv using streamreader

Question

I have my following code to read values from CSV file and do some processing. I would like to skip the first row of the input CSV file as it contains header text but I'd want to add it back after the processing is done.

List<string> values = new List<string>();
using (StreamReader sr = new StreamReader(filePath))
{
    while (sr.Peek() != -1)
    {
        string line = sr.ReadLine();
        List<string> lineValues = line.Split(',').ToList();
        var tempMinInt = 1;
        var tempValue = 1;
        var tempValInt = Convert.ToInt32(lineValues[4]);
        if (lineValues[3] == "1876")
        {
            if (tempValInt % 60 != 0)
            {
                tempMinInt = (tempValInt / 60) + 1;
                tempValue = tempMinInt * 30;
            }
            else
            {
                tempMinInt = tempValInt / 60;
                tempValue = tempMinInt * 30;
            }
        }
        else if (lineValues[3] == "1875")
        {
            if (tempValInt != 0)
            {
                tempValue = 500;
            }
            else
                tempValue = 0;
        }

        if (lineValues[3] == "1876")
        {
            values.Add(string.Join(",", lineValues) + "," + "0" + "," + "30" + "," + tempValue.ToString());
        }
        else if (lineValues[3] == "1875")
        {
            values.Add(string.Join(",", lineValues) + "," + "1" + "," + "500" + "," + tempValue.ToString());
        }

    }
}

Sample input csv looks like this:

id, datetime, msisdn, num, duration
33083,2011-12-19 05:17:57+06:30,98590149,1875,258
33084,2011-12-19 05:22:28+06:30,98590149,1875,69
33085,2011-12-19 05:23:45+06:30,98590149,1875,151
33086,2011-12-19 05:30:21+06:30,98590149,1875,58
33087,2011-12-19 06:44:19+06:30,949826259,1875,66

And I'd like to have my output like this:

id, datetime, msisdn, num, duration, type, ammount, total
33083,2011-12-19 05:17:57+06:30,98590149,1875,258,1,500,500
33084,2011-12-19 05:22:28+06:30,98590149,1875,69,1,500,500
33085,2011-12-19 05:23:45+06:30,98590149,1875,151,1,500,500
33086,2011-12-19 05:30:21+06:30,98590149,1875,58,1,500,500

Jon Skeet · Accepted Answer · 2024-10-17 06:46:49Z

82

Just read it first before you get into the loop. I'd do this:

using (StreamReader sr = new StreamReader(filePath))
{
    string headerLine = sr.ReadLine();
    string line;
    while ((line = sr.ReadLine()) != null)
    {
         ...
    }
}

(I don't like using Peek, personally.)

Then when you write out the output, start with headerLine.

As of C# 7, pattern matching makes this more pleasant:

using (StreamReader sr = new StreamReader(filePath))
{
    string headerLine = sr.ReadLine();
    while (sr.ReadLine() is string line)
    {
          ...
    }
}

edited Oct 17, 2024 at 6:46

answered Feb 1, 2012 at 9:11

Jon Skeet

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5 Comments

Justin Over a year ago

I rarely, if ever use Peek, but just curious...why don't you like using Peek?

Jon Skeet Over a year ago

@Justin: I tend to worry that there's a possibility of the data changing when you next read it - it feels cleaner to "read once and act" than to "read, check, then read again" and assume that the two reads will have the same results. It's entirely possible that the buffering details of whatever abstraction is in use (StreamReader in this case) can guarantee the result of Peek is consistent with the next read, but it feels cleaner not to have to worry about that.

ChuckNeuros Over a year ago

Downvoting this because gdoron's suggestion below of not allocating a variable is so much less disturbing than having a dangling variable and I want his response to rise.

Jon Skeet Over a year ago

@ChuckNeuros: That's a choice, I guess... I've added in a nicer version (IMO) using pattern matching, although that still introduces the variable into the parent scope. Personally I'm less bothered by that than something that genuinely makes a difference at execution time (calling Peek and then ReadLine) but each to their own. I'd be very surprised to see enough votes cast on answers to a 12-year-old question to change the answer order though...

gdoron Over a year ago

@JonSkeet ROFL... Yeah, and I'm not sure how my answer is "better", it's just a matter of style and taste.

gdoron · Accepted Answer · 2012-02-01 09:11:35Z

23

Just read the first line and do nothing with it...

List<string> values = new List<string>();
using (StreamReader sr = new StreamReader(filePath))
{
    sr.ReadLine();
    while (sr.Peek() != -1)
    {
        string line = sr.ReadLine();
        List<string> lineValues = line.Split(',').ToList();

        //***//
    }
}

answered Feb 1, 2012 at 9:11

gdoron

151k59 gold badges302 silver badges376 bronze badges

1 Comment

ChuckNeuros Over a year ago

Oh yes this is so much more pleasant than having a pointless variable allocated!!! More upvotes, please. Even if the compiler is smart enough to instantly destroy it, having an unused variable is ugly and confusing.

Arion · Accepted Answer · 2012-02-01 09:17:57Z

6

Something like this:

bool isFirst=true;
using (StreamReader sr = new StreamReader(filePath))
{
    while (sr.Peek() != -1)
    {
        if(isFirst)
        {
            isFirst=false;
            continue;
        }
    }
}

answered Feb 1, 2012 at 9:17

Arion

31.3k10 gold badges75 silver badges89 bronze badges

Comments

Muhammad Faiq · Accepted Answer · 2020-04-17 06:51:20Z

2

I recommend, to use technique to handle such situation,

                int row = 0;
                using (StreamReader sr = new StreamReader(filePath))

                {
                   While(reader.Read()) //Each row of the file
                    {
                        row++;
                        if(row==1)
                        {
                            continue;
                        }
               }
... code..
}

answered Apr 17, 2020 at 6:51

Muhammad Faiq

691 bronze badge

Comments

cjk · Accepted Answer · 2012-02-01 09:11:32Z

1

You could read the first line before your while loop and store it, or you could use a counter / boolean field to check where in the file you are.

answered Feb 1, 2012 at 9:11

cjk

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Comments

LUCKY MOSERI · Accepted Answer · 2023-10-23 07:51:52Z

-1

When lineNumber is 1, it will skip the execution part and not process anything from first row.   


string doWork = string.Empty;

   var lineNumber = 1;

   using (StreamReader reader = new StreamReader(fileLocation))
            {
                while (!reader.EndOfStream)
                {
                    var line = reader.ReadLine();

                    var docLine = line.Split(',');

                    if (!String.IsNullOrEmpty(line.ToString()))
                    {
                        if (lineNumber != 0)
                        {
                            if (lineNumber > 1)
                            {
                                doWork = "Excecuting";
                            }
                        }
                        lineNumber++;
                    }
                }
            }

answered Oct 23, 2023 at 7:51

LUCKY MOSERI

1

1 Comment

Community Over a year ago

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