How to not write duplicate values to csv file [duplicate]

Question

I am trying to find a better way to write data to csv file. Right now every loop iteration appends the headers and data to file like below

I want to modify my logic so that I get only the data like.

Any tips on what I can change are highly appreciated. Thanks

......
var csvContent = new StringBuilder();
csvContent.AppendLine("ONE, TWO, THREE);
var csvPath = defaultFilePath + "file7.csv";
foreach (var i in values)
{
    fileData.DataOne = i["DataPointOne"].ToString();
    fileData.DataTwo = i["DataPointTwo"].ToString();
    fileData.DataThree = DateTime.Parse(i["DataPointThree"]);
    csvContent.AppendLine(fileData.DataOne + "," + fileData.DataTwo + "," + fileData.DataThree);
    File.AppendAllText(csvPath, csvContent.ToString());
}
......

@MathiasR.Jessen, i tried that. The file does not get written. — Maddy
– Maddy, Commented Mar 1, 2018 at 16:08
Based on title this is duplicate of stackoverflow.com/questions/2537823/…, but really is just standard "how to write CSV to file in C#" like stackoverflow.com/questions/18757097/… which shows exactly the same code you trying to do, just with proper placement of writing result of building string to file. (Likely you are not doing it anyway for actual code and using a library to do read/write CSV, but it is ok to ask questions for entertainment/education purposes) — Alexei Levenkov
– Alexei Levenkov, Commented Mar 1, 2018 at 16:42

waka · Accepted Answer · 2018-03-01 16:10:57Z

4

You constantly append lines to csvContent and then write it all to the file with every iteration. Get rid of the StringBuilder (it isn't really needed here) and use a StreamWriter like this:

using(var streamWriter = new StreamWriter("path\\toFile.csv")) 
{
    streamWriter.WriteLine("ONE, TWO, THREE");
    foreach (var i in values)
    {
        fileData.DataOne = i["DataPointOne"].ToString();
        fileData.DataTwo = i["DataPointTwo"].ToString();
        fileData.DataThree = DateTime.Parse(i["DataPointThree"]);
        streamWriter.WriteLine(fileData.DataOne + "," + fileData.DataTwo + "," + fileData.DataThree);
    }
}

answered Mar 1, 2018 at 16:10

waka

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1 Comment

Maddy Over a year ago

Thank you very much for the help. I will read up on streamwriter and stringbuilder.

Pavel Sem · Accepted Answer · 2018-03-01 16:34:23Z

1

Problem is that there is same StringBuilder content is stored into file multiple times.

Iteration 1 csvContent contains data for line 1 --> line 1 is stored to file. File contains line 1

Iteration 2 csvContent is appended with line 2 --> line 1, 2 is appended stored into file. File contains line 1, 1, 2

Iteration 3 csvContent is appended with line 3 --> line 1, 2, 3 is again appended to file. File contains line 1, 1, 2, 1, 2, 3

Simple fix should be to store the file outside the loop or use e.g. StreamWriter suggested in the other answer.

answered Mar 1, 2018 at 16:34

Pavel Sem

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