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Fluent CSV

A .NET library for read your csv files in a fluent way.


  • Written in .NET Standard (can be used in all your .NET projects including .NET Core, Xamarin, Mono, and other...)
  • Implements RFC 4180
  • Free and Open source
  • Ease of reading and writing code (don't just do the right thing, but also says the right thing)
  • Automatically generates an error row report, customizable with your validation rules

What's new ?

FluentCSV 3.0 is now available with a big performance improvement!

  • The speed of the Rfc4180 parser is multiplied by 8.
  • The SimpleParsingMode gains 20% of performance.

Thus, with this new version, you can read a CSV file of 1 000 000 lines in just a few seconds!

See more details here.

Adding FluentCSV to your project

You can use NuGet to quickly add FluentCSV to your project. Just search for 'FluentCSV' and install the package, or type the following command into 'Package Manager Console'

PM> Install-Package FluentCsv

Basic usage

Imagine a csv file named "sample1.csv"


This is how to read your file using Fluent CSV

var csv = Read.Csv.FromFile("sample1.csv")
	.ThatReturns.ArrayOf<(string Name, int Age)>()
	.Put.Column("name").Into(a => a.Name)
	.Put.Column("age").As<int>().Into(a => a.Age)

Console.WriteLine("CSV DATA");
csv.ResultSet.ForEach(r=> Console.WriteLine($"Name : {r.Name} - Age : {r.Age}"));

csv.Errors.ForEach(e => Console.WriteLine($"Error at line {e.LineNumber} column index {e.ColumnZeroBasedIndex} : {e.ErrorMessage}"));


Name : Smith - Age : 43
Name : Robin - Age : 38
Error at line 4 column index 1 : The format of the input string is incorrect.


API Structure


Choose the encoding of your data. This method is optional. Default encoding is UTF8

Method Argument(s)
EncodedIn [Encoding]

Select a way to read your csv data. You can choose only one of the following methods

Method Argument(s) Comment
FromString [CsvString] Read a csv directly from a string.
FromFile [FilePath] Read a csv from a file.
FromAssemblyResource [ResourceName] (Assembly) Read a csv from an assembly resource. If assembly is not defined, the API get the resource from the calling assembly.
FromStream [Stream] Read a csv from a stream.
FromBytes [ByteArray] Read a csv from a byte array.


Define optional CSV configuration which can be combined with the And keyword

Method Argument(s) Comment Usage Default value
ColumnsDelimiter [DelimiterString] Define the string used as columns delimiter. Optional ;
EndOfLineDelimiter [DelimiterString] Define the string used as new line delimiter. Optional Environment.NewLine
Header (CaseMode) Declare the first line as header. You can specify if you treat it as case sensitive or case insensitive when putting columns in properties. Optional CaseInsensitive
SimpleParsingMode no argument By default, FluentCsv use the RFC 4180 for parse your csv file. You can use SimpleParsingMode if your file doesn't respect it and you notice some problem with double quote. Optional NC
CultureInfo [CultureCode] Some data like date or decimal numbers are not the same according to the culture. For example french people use a comma as decimal separator while US people use a dot character. By defining the culture code, you can tel to FluentCsv how to parse this types. Optional CurrentCulture


Define what kind of object to returns as resultset and how to populate them.
The type must be a class with a parameterless constructor, and contains properties with public getter and setter, or a tuple like (string a,int b).
Due to a limitation of the ValueTuple<> generic type, use a POCO instead of a tuple if your result contains more than 7 members.

You must choose one of the following methods.

Method Argument(s) Comment
ArrayOf<T> [Type of class used to store csv data] Define the result set as a T[] array
DictionaryOf<T> [Type of class used to store csv data] [Member to use as a Key] Define the result set as a Dictionary<object,T>. The Key will be the member passed as argument.


Define how to map each column with a property.

Method Argument(s) Comment Usage
Column [Index or HeaderName] When a column is defined by HeaderName, FluentCsv consider implicitly that the first line is a header. If all columns are defined by index and you want to skip the first line, you can use the With.Header() method to do it. Mandatory
Method Argument(s) Comment Usage Default Value
MakingSureThat [ValidationFunction] Set a function which validate the format of the column data. Using this method is more readable and increase performance for data validation instead of throwing exceptions. Optional Data.Valid
As<T> [DestinationType] Define the destination type. Optional string
InThisWay [ConversionFunction] Set how to convert the csv column string data into the destination type. If not defined, a default conversion depending on culture info is applied. Optional Convert.ChangeType
Into [TargetProperty] Set in which property to put the converted data. The property must be the same type of As<T> and have a public setter. Also, you can define a property localised in a subclass of your result providing that it's correctly instantiated. (see example A) Mandatory NC


Execute the csv parsing and return two collections

  • ResultSet : Contains all lines of your csv that are correctly parsed.
  • Errors : Contains all errors while parsing your file, including line number, column zero base index, column name (if csv contains header line) and exception message.

You can call the SaveErrorsInFile(filePath) methods to write all errors in a simple file report. The output is a csv file structured as follow :

1;0;"test";"number ""1"" is invalid"

Some scenarios

Example A - Populate POCO with hierarchical objects

  • A csv file with contact information
  • BirthDate is in US format (Month/day/year)
  • We want to store Firstname,Lastname and Birthdate in a subclass named Contact
  • We want to store Street, City and ZipCode in an other subclass named Address

Csv file

Rosemary;Berube;04/10/1983;2435 Leverton Cove Road;Springfield;01103
Richard;Lewis;12/11/1944;1509 Big Elm;New York;64110
Michael;Lindquist;12/21/1939;1334 Clark Street;Chicago;60607


public class CsvInfos
	public Contact Contact { get; } = new Contact();
	public Address Address { get; } = new Address();

	public override string ToString() => $"{Contact} - {Address}";

public class Contact
	public string Firstname { get; set; }
	public string Lastname { get; set; }
	public DateTime BirthDate { get; set; }

	public override string ToString() => $"{Firstname} {Lastname} ({BirthDate:d})";

public class Address
	public string Street { get; set; }
	public string City { get; set; }
	public string ZipCode { get; set; }

	public override string ToString() => $"City : {City}";

API Call

var csv = Read.Csv.FromFile("exampleA.csv")
     .Put.Column("FirstName").Into(p => p.Contact.Firstname)
     .Put.Column("LastName").Into(p => p.Contact.Lastname)
     .Put.Column("BirthDate").As<DateTime>().Into(p => p.Contact.BirthDate)
     .Put.Column("Street").Into(p => p.Address.Street)
     .Put.Column("City").Into(p => p.Address.City)
     .Put.Column("ZipCode").Into(p => p.Address.ZipCode)

Console.WriteLine("CSV DATA");


Rosemary Berube (10/04/1983) - City : Springfield
Richard Lewis (11/12/1944) - City : New York
Michael Lindquist (21/12/1939) - City : Chicago

Example B - Parse a csv file that look crazy

  • A csv file where columns are separated with '-' and lines end with '#'.
  • There are two columns where headers have same name (but not same case)
  • Some data have a double quote, and we want to get it

Csv file


API Call

var csv = Read.Csv.FromFile("exampleB.csv")
	.ThatReturns.ArrayOf<(string FirstName, string LastName)>()
	.Put.Column("NAME").Into(a => a.FirstName)
	.Put.Column("name").Into(a => a.LastName)

Console.WriteLine("CSV DATA");
csv.ResultSet.ForEach(a=>Console.WriteLine($"{a.FirstName} {a.LastName}"));


Smith Bob
Rob"in Wiliam

Example C - Data validation

  • A csv file without header that contains information with validation rules and structured data
  • The file is a csv generated by excel, with columns separated by tabulation
  • First column is an Id, second a phone number, third an enumeration and fourth a multiline address
  • The id is a number
  • Phone numbers that not contains 10 digits are not valid
  • The enumeration is a set of letters (A, B or F) separated by pipes character '|'. All other letters are invalid

Csv file

1	0309545655	A	"1344 Wright Court
Birmingham, AL 35209"
2	0988767454	A|B	"2253 Jadewood Drive
South Bend, IN 46625"
A	0166245163	B|F	"2920 Hood Avenue
San Diego, CA 92103"
4	0562435562	F	"3066 Maple Avenue
Coeur D Alene, ID 83814"
5	0261726323	A|C	"2992 Victoria Court
Pittsfield, ME 04967"
6	0493928372	F|B|A	"667 Anthony Avenue
Abilene, TX 79601"
7	046768778A	A|F	"2438 Logan Lane
Lakewood, CO 80214"
8	0799878757	B|A	"4105 Asylum Avenue
Bridgeport, CT 06604"
9	0805546766	B	"252 Hinkle Deegan Lake Road
Lexington, KY 40505"
10	0487876876	F	"1081 Brookview Drive
Beaumont, TX 77701"

First possibility : using POCOs, Value objects and Exceptions


public class LineExampleC
	public int Id { get; set; }
	public PhoneNumber PhoneNumber { get; set; }
	public CustomEnum CustomEnum { get; set; }
	public string Address { get; set; }

	public override string ToString()
	    => $"id = {Id}, Phone = {PhoneNumber}, Enum = {CustomEnum}, Address = {Address}";

public class PhoneNumber
	private readonly string _phoneNumber;

	public PhoneNumber(string phone)
		throw new ArgumentException("Phone number is invalid");

	    _phoneNumber = phone;

	public override string ToString()
	    => _phoneNumber;

public class CustomEnum
	private List<string> _enumList;

	public CustomEnum(string @enum)
	    _enumList = @enum.Split('|').ToList();
	    if(!_enumList.TrueForAll(a => a == "A" || a == "B" || a == "F"))
		throw new ArgumentException("Invalid enum character");

	public override string ToString()
	    => string.Join(" and ", _enumList);

API Call

var csv = Read.Csv.FromFile("exampleC.csv")
      .Put.Column(0).As<int>().Into(a => a.Id)
      .Put.Column(1).As<PhoneNumber>().InThisWay(s => new PhoneNumber(s)).Into(a => a.PhoneNumber)
      .Put.Column(2).As<CustomEnum>().InThisWay(s => new CustomEnum(s)).Into(a => a.CustomEnum)
      .Put.Column(3).Into(a => a.Address)

Console.WriteLine("CSV DATA");

csv.Errors.ForEach(e => Console.WriteLine($"Error at line {e.LineNumber} column index {e.ColumnZeroBasedIndex} : {e.ErrorMessage}"));

Second possibility (since version 2.0) : using MakingSureThat and Tuple

API Call

 var csv = Read.Csv.FromFile(file)
    .ThatReturns.ArrayOf<(int Id, string PhoneNumber, string CustomEnum, string Address)>()
    .Put.Column(0).As<int>().Into(a => a.Id)
    .Put.Column(1).MakingSureThat(PhoneNumberIsValid).Into(a => a.PhoneNumber)
    .Put.Column(2).MakingSureThat(EnumIsValid).InThisWay(a=>a.Replace("|"," and ")).Into(a => a.CustomEnum)
    .Put.Column(3).Into(a => a.Address)

Console.WriteLine("CSV DATA");
csv.ResultSet.ForEach(a=>Console.WriteLine($"id = {a.Id}, Phone = {a.PhoneNumber}, Enum = {a.CustomEnum}, Address = {a.Address}"));

csv.Errors.ForEach(e => Console.WriteLine($"Error at line {e.LineNumber} column index {e.ColumnZeroBasedIndex} : {e.ErrorMessage}"));

Data PhoneNumberIsValid(string phone)
    =>  Regex.IsMatch(phone, "[0-9]{10}")
            ? Data.Valid 
            : Data.Invalid("Phone number is invalid");

Data EnumIsValid(string @enum)
    => @enum.Split('|').ToList().TrueForAll(a => a == "A" || a == "B" || a == "F")
        ? Data.Valid
        : Data.Invalid("Invalid enum character");

Output (in both case)

id = 1, Phone = 0309545655, Enum = A, Address = 1344 Wright Court
Birmingham, AL 35209
id = 2, Phone = 0988767454, Enum = A and B, Address = 2253 Jadewood Drive
South Bend, IN 46625
id = 4, Phone = 0562435562, Enum = F, Address = 3066 Maple Avenue
Coeur D Alene, ID 83814
id = 6, Phone = 0493928372, Enum = F and B and A, Address = 667 Anthony Avenue
Abilene, TX 79601
id = 8, Phone = 0799878757, Enum = B and A, Address = 4105 Asylum Avenue
Bridgeport, CT 06604
id = 9, Phone = 0805546766, Enum = B, Address = 252 Hinkle Deegan Lake Road
Lexington, KY 40505
id = 10, Phone = 0487876876, Enum = F, Address = 1081 Brookview Drive
Beaumont, TX 77701

Error at line 3 column index 0 : The format of the input string is incorrect.
Error at line 5 column index 2 : Invalid enum character
Error at line 7 column index 1 : Phone number is invalid

Change log

3.0.0 - 2021/06/12

  • [Improvement] Upgrade to .Net Standard 2.1
  • [Improvement] Rewriting for best performances (see the benchmark)

2.0.1 - 2021/03/03

  • [BugFix] Error on linux when reading last column due to default line delimiter

2.0.0 - 2020/10/23

  • [Feature] MakingSureThat
  • [Improvement] Accepting Tuple as resultset

1.1.0 - 2018/09/05

  • [Feature] Read.Csv.EncodedIn
  • [Feature] Read.Csv.FromBytes
  • [Feature] Read.Csv.FromStream
  • [Feature] ThatReturns.DictionaryOf<T>(d => d.KeyMember)
  • [Feature] SaveErrorsInFile method.

1.0.2 - 2018/08/24

  • [BugFix] Bad parsing for quadruple quotes

1.0.1 - 2018/08/22

  • [BugFix] Incorrect parsing if string start with UTF8 BOM
  • [BugFix] Error when using a pipe as column delimiter

1.0.0 - 2018/08/17

  • First release of the library


FluentCSV is licensed under MIT License, which means it is free for all of your products, including commercial software.


Read your CSV files in a fluent way








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