Reading only specific columns from a CSV file out of many

Question

I have a CSV file which looks like this basically:

TransactionID         ProfileID       Date           // more columns here...
somevalue             1231231         


        

Answer 1

Hi You may use this code snippets to read any kind of csv file with little customization according to your needs.

public class CsvRow : List<string>
{
    public string LineText { get; set; }
}


public class CsvFileReader : StreamReader
{
    public CsvFileReader(Stream stream)
        : base(stream)
    {
    }

    public CsvFileReader(string filename)
        : base(filename)
    {
    }

    public bool ReadRow(CsvRow row,char separator)
    {
        try
        {
            row.LineText = ReadLine();
            if (String.IsNullOrEmpty(row.LineText))
                return false;

            int pos = 0;
            int rows = 0;

            while (pos < row.LineText.Length)
            {
                string value;

                // Special handling for quoted field
                if (row.LineText[pos] == '"')
                {
                    // Skip initial quote
                    pos++;

                    // Parse quoted value
                    int start = pos;
                    while (pos < row.LineText.Length)
                    {
                        // Test for quote character
                        if (row.LineText[pos] == '"')
                        {
                            // Found one
                            pos++;

                            // If two quotes together, keep one
                            // Otherwise, indicates end of value
                            if (pos >= row.LineText.Length || row.LineText[pos] != '"')
                            {
                                pos--;
                                break;
                            }
                        }
                        pos++;
                    }
                    value = row.LineText.Substring(start, pos - start);
                    value = value.Replace("\"\"", "\"");
                }
                else
                {
                    // Parse unquoted value
                    int start = pos;
                    while (pos < row.LineText.Length && row.LineText[pos] != separator)
                        pos++;
                    value = row.LineText.Substring(start, pos - start);
                }

                // Add field to list
                if (rows < row.Count)
                    row[rows] = value;
                else
                    row.Add(value);
                rows++;

                // Eat up to and including next comma
                while (pos < row.LineText.Length && row.LineText[pos] != separator)
                    pos++;
                if (pos < row.LineText.Length)
                    pos++;
            }
            // Delete any unused items
            while (row.Count > rows)
                row.RemoveAt(rows);

            // Return true if any columns read
            return (row.Count > 0);
        }
        catch (Exception ex)
        {
            ex.ToString();
            throw;
        }
    }
}  

Than just call the function as follows

using (CsvFileReader reader = new CsvFileReader(filePath))
            {
                char separator = ';'; //CSV file separated by (in this case it is semicolon)
                List<MyMappedCSVFile> lst=new List<MyMappedCSVFile>();
                CsvRow row = new CsvRow();
                while (reader.ReadRow(row,separator))
                {  
                    if (row[0].Equals("TransactionID")) //to skip header
                        continue;
                    else
                    {
                       MyMappedCSVFile obj=new MyMappedCSVFile();
                       obj.ProfileID =row[1]; //Column Index of ProfileID
                       obj.Date = row[2]; // Column index of Date 
                       lst.Add(obj);
                    }
                }
            }  

filePath is the path for your csv file

Answer 2

The header is still to skip in this code, but with this code, you can choose which columns to extract. It might be much faster if you use a StreamReader. And you will need a constructor for your object.

var temp = File.ReadAllLines(@"C:\myFile.csv");
public List<MyMappedCSVFile>() myExtraction = new List<MyMappedCSVFile>();
foreach(string line in temp)
{
  var delimitedLine = line.Split('\t'); //set ur separator, in this case tab

  myExtraction.Add(new MyMappedCSVFile(delimitedLine[0], delimitedLine[3]));
}

Code for your Object:

public class MyMappedCSVFile
{
  public string ProfileID { get; set; } 
  public string Date { get; set; }

  public MyMappedCSVFile(string profile, string date)
  {
    ProfileID = profile;
    Date = date;
  }
}

Answer 3

CsvHelper is a nice package you can use for this sort of thing, it lets you get by index or name.

An example from the documents is

// Don't forget to read the data before getting it.
csv.Read();

// By position
var field = csv[0];

// By header name
var field = csv["HeaderName"];

The docs give lots of examples of reading the file and iterating over it, and mapping to classes and so on. Seems perfect for this.

https://github.com/JoshClose/CsvHelper

Here is a more complete answer to your solution in realtion to reading (as you have installed the package)

    TextReader fileReader = File.OpenText(somepath);
    var csv = new CsvReader(fileReader);
    var records = csv.GetRecords<MyMappedCSVFile>();

records will be a list of your CSV rows mapped to your object.