How to apply changes to a specific column in the CSV file?

Question

Within my CSV file I have a column which holds a string and a date time type. Which is the 5th column in my CSV file which has this data (TUI 01/01/01). I applied some changes in order to a comma on the space to separate this value in two different columns(TUI,01/01/01). However, these changes affect other column data which have a space between their values. I would just like to apply these changes only to affect the fifth column.

Any suggestion would be much appreciating.

 static void Main(string[] args)
    {
        var filePath = Path.Combine(Directory.GetCurrentDirectory(), "InventoryReport 02_08_2016.csv");
        var fileContents = ReadFile(filePath);
        foreach (var line in fileContents)
        {
            Console.WriteLine(line);
        }

        Console.WriteLine("Press any key to exit...");
        Console.ReadKey();
    }

    public static IList<string> ReadFile(string fileName)
    {
        var results = new List<string>();

        var target = File
 .ReadAllLines(fileName)
 .Skip(1) // Skip the line with column names
 .Select(line => line.Replace(' ', ',')); // ... splitting  pattern

        // Writing back to some other file
        File.WriteAllLines(fileName, target);

        return results;
    }
}

Answer 1

ok you are clearly applying that replace to whole file that's why it's affecting all the columns, try another way :
-loop each line
-in each loop split elements using commas

var lineElements = line.split(',');

-and then specifically apply that to 5th column :

var fifthElement = lineElements[4].Replace(' ', ',');

-that will apply the effect only on 5th element
-combine it up and get whole line as you were

Answer 2

Your current way is affecting the whole line( .Select(line => line.Replace(' ', ',')) ), not just the 5th field on the line. Here's another way.

Option 1

    public Form1()
    {
        InitializeComponent();
        ReWriteFile(@"M:\StackOverflowQuestionsAndAnswers\38873875\38873875\testdata.csv");//call the method
    }

    public void ReWriteFile(string fileName)
    {
        using (StreamWriter sw = new StreamWriter(@"M:\StackOverflowQuestionsAndAnswers\38873875\38873875\testdata_new.csv"))
        {
            string currentLine = string.Empty;
            using (StreamReader sr = new StreamReader(fileName))//
            {
                while ((currentLine = sr.ReadLine()) != null)//while there are lines to read
                {
                    string[] fielded = currentLine.Split(',');//split your fields into an array
                    fielded[4] = fielded[4].Replace(" ", ",");//replace the space in position 4(field 5) of your array
                    sw.WriteLine(string.Join(",", fielded));//write the line in the new file
                }
            }
        }

    }

My starting data was this( there is a mismatch in column counts, but it does not keep anything from working as it should for the purpose of this question ):

col1,col2,col3,col4,col5,col6
col 1 data,col 2 data,col 3 data,col 4 data,TUI 01/01/01,col 5 data,col 6 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI 01/01/01,col 5 data,col 6 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI 01/01/01,col 5 data,col 6 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI 01/01/01,col 5 data,col 6 data

It became this after it went through the method:

col1,col2,col3,col4,col5,col6
col 1 data,col 2 data,col 3 data,col 4 data,TUI,01/01/01,col 5 data,col 6 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI,01/01/01,col 5 data,col 6 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI,01/01/01,col 5 data,col 6 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI,01/01/01,col 5 data,col 6 data

After reading your question here how to display the column names on my csv file I realized you must be skipping the first row for a good reason so I updated my code to do so and to fix your question's problem at the same time.

This option writes the header record as-is

    /// <summary>
    /// In this method I use the lineCounter as my position tracker to know which line I'm readin at the time
    /// </summary>
    /// <param name="fileName"></param>
    public void ReWriteFileDontAffectFirstRow(string fileName)
    {
        int lineCounter = 0;//lets make our own position tracker
        using (StreamWriter sw = new StreamWriter(@"M:\StackOverflowQuestionsAndAnswers\38873875\38873875\testdata_new2.csv"))
        {
            string currentLine = string.Empty;
            using (StreamReader sr = new StreamReader(fileName))
            {
                while ((currentLine = sr.ReadLine()) != null)//while there are lines to read
                {
                    if (lineCounter != 0)
                    {
                        //If it's not the first line
                        string[] fielded = currentLine.Split(',');//split your fields into an array
                        fielded[4] = fielded[4].Replace(" ", ",");//replace the space in position 4(field 5) of your array
                        sw.WriteLine(string.Join(",", fielded));//write the line in the new file
                    }
                    else
                    {
                        //If it's the first line
                        sw.WriteLine(currentLine);//Write the line as-is
                    }
                    lineCounter++;
                }
            }
        }
    }

Original data was this( there is a mismatch in column counts, but it does not keep anything from working as it should for the purpose of this question )

col 1,col 2,col 3,col 4,col 5,col 6
col 1 data,col 2 data,col 3 data,col 4 data,TUI 01/01/01,col 5 data,col 6 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI 01/01/01,col 5 data,col 6 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI 01/01/01,col 5 data,col 6 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI 01/01/01,col 5 data,col 6 data

Data after going through the method

col 1,col 2,col 3,col 4,col 5,col 6
col 1 data,col 2 data,col 3 data,col 4 data,TUI,01/01/01,col 5 data,col 6 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI,01/01/01,col 5 data,col 6 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI,01/01/01,col 5 data,col 6 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI,01/01/01,col 5 data,col 6 data

This option adds a field to the header record

    public void ReWriteFileAdjustHeaderRecordToo(string fileName)
    {
        int lineCounter = 0;//lets make our own position tracker
        using (StreamWriter sw = new StreamWriter(@"M:\StackOverflowQuestionsAndAnswers\38873875\38873875\testdata_new3.csv"))
        {
            string currentLine = string.Empty;
            using (StreamReader sr = new StreamReader(fileName))
            {
                while ((currentLine = sr.ReadLine()) != null)//while there are lines to read
                {
                    List<string> fielded = new List<string>(currentLine.Split(','));//splits your fields into a list of fields. This is no longer a string[]. Its a list so we can "inject" the new column in the header record.
                    if (lineCounter != 0)
                    {
                        //If it's not the first line
                        fielded[4] = fielded[4].Replace(" ", ",");//replace the space in position 4(field 5) of your array
                        sw.WriteLine(string.Join(",", fielded));//write the line in the new file
                    }
                    else
                    {
                        //If it's the first line
                        fielded.Insert(4, "new inserted col");//inject the new column into the list
                        sw.WriteLine(string.Join(",", fielded));//write the line in the new file
                    }
                    lineCounter++;
                }
            }
        }
    }

Starting data( this data has the right starting column count )

col 1,col 2,col 3,col 4,col 5,col 6
col 1 data,col 2 data,col 3 data,col 4 data,TUI 01/01/01,col 5 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI 01/01/01,col 5 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI 01/01/01,col 5 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI 01/01/01,col 5 data

Data after the method

col 1,col 2,col 3,col 4,new inserted col,col 5,col 6
col 1 data,col 2 data,col 3 data,col 4 data,TUI,01/01/01,col 5 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI,01/01/01,col 5 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI,01/01/01,col 5 data
col 1 data,col 2 data,col 3 data,col 4 data,TUI,01/01/01,col 5 data