Sep - Possibly the World's Fastest .NET CSV Parser
Modern, minimal, fast, zero allocation, reading and writing of separated values
(csv, tsv etc.). Cross-platform, trimmable and AOT/NativeAOT compatible.
Featuring an opinionated API design and pragmatic implementation targetted at
machine learning use cases.
🔎 Minimal - a succinct yet expressive API with few options and no hidden
changes to input or output. What you read/write is what you get. This means
there is no "automatic" escaping/unescaping of quotes, for example.
🚀 Fast - blazing fast with both architecture specific and cross-platform
SIMD vectorized parsing incl. 64/128/256/512-bit paths e.g. AVX2, AVX-512 (.NET
8.0+), NEON. Uses csFastFloat for
fast parsing of floating points. Reads or writes one row at a time efficiently
with detailed benchmarks to prove it.
🗑️ Zero allocation - intelligent and efficient memory management allowing
for zero allocations after warmup incl. supporting use cases of reading or
writing arrays of values (e.g. features) easily without repeated allocations.
🌐 Cross-platform - works on any platform, any architecture supported by
.NET. 100% managed and written in beautiful modern C#.
✂️ Trimmable and AOT/NativeAOT compatible - no problematic reflection or
dynamic code generation. Hence, fully
trimmable
and
Ahead-of-Time
compatible. With a simple console tester program executable possible in just a
few MBs. 💾
🗣️ Opinionated and pragmatic - conforms to the essentials of
RFC-4180, but takes an opinionated and
pragmatic approach towards this especially with regards to quoting and line
ends. See section RFC-4180.
var text = """
A;B;C;D;E;F
Sep;🚀;1;1.2;0.1;0.5
CSV;✅;2;2.2;0.2;1.5
""";
using var reader = Sep.Reader().FromText(text); // Infers separator 'Sep' from header
using var writer = reader.Spec.Writer().ToText(); // Writer defined from reader 'Spec'
// Use .FromFile(...)/ToFile(...) for files
var idx = reader.Header.IndexOf("B");
var nms = new[] { "E", "F" };
foreach (var readRow in reader) // Read one row at a time
{
var a = readRow["A"].Span; // Column as ReadOnlySpan<char>
var b = readRow[idx].ToString(); // Column to string (might be pooled)
var c = readRow["C"].Parse<int>(); // Parse any T : ISpanParsable<T>
var d = readRow["D"].Parse<float>(); // Parse float/double fast via csFastFloat
var s = readRow[nms].Parse<double>(); // Parse multiple columns as Span<T>
// - Sep handles array allocation and reuse
foreach (ref var v in s) { v *= 10; }
using var writeRow = writer.NewRow(); // Start new row. Row written on Dispose.
writeRow["A"].Set(a); // Set by ReadOnlySpan<char>
writeRow["B"].Set(b); // Set by string
writeRow["C"].Set($"{c * 2}"); // Set via InterpolatedStringHandler, no allocs
writeRow["D"].Format(d / 2); // Format any T : ISpanFormattable
writeRow[nms].Format(s); // Format multiple columns directly
// Columns are added on first access as ordered, header written when first row written
}
var expected = """
A;B;C;D;E;F
Sep;🚀;2;0.6;1;5
CSV;✅;4;1.1;2;15
"""; // Empty line at end is for line ending,
// which is always written.
Assert.AreEqual(expected, writer.ToString());
// Above example code is for demonstration purposes only.
// Short names and repeated constants are only for demonstration.
Naming and Terminology
Sep uses naming and terminology that is not based on RFC-4180, but
is more tailored to usage in machine learning or similar. Additionally, Sep
takes a pragmatic approach towards names by using short names and abbreviations
where it makes sense and there should be no ambiguity given the context. That
is, using Sep for Separator and Col for Column to keep code succinct.
Term
Description
Sep
Short for separator, also called delimiter. E.g. comma (,) is the separator for the separated values in a csv-file.
Header
Optional first row defining names of columns.
Row
A row is a collection of col(umn)s, which may span multiple lines. Also called record.
Col
Short for column, also called field.
Line
Horizontal set of characters until a line ending; \r\n, \r, \n.
Index
0-based that is RowIndex will be 0 for first row (or the header if present).
Number
1-based that is LineNumber will be 1 for the first line (as in notepad). Given a row may span multiple lines a row can have a From line number and an ToExcl line number matching the C# range indexing syntax [LineNumberFrom..LineNumberToExcl].
Application Programming Interface (API)
Besides being the succinct name of the library, Sep is both the main entry
point to using the library and the container for a validated separator. That is,
Sep is basically defined as:
public readonly record struct Sep(char Separator);
The separator char is validated upon construction and is guaranteed to be
within a limited range and not being a char like " (quote) or similar. This
can be seen in src/Sep/Sep.cs. The separator is constrained
also for internal optimizations, so you cannot use any char as a separator.
⚠ Note that all types are within the namespace nietras.SeparatedValues and not
Sep since it is problematic to have a type and a namespace with the same name.
To get started you can use Sep as the static entry point to building either a
reader or writer. That is, for SepReader:
using var reader = Sep.Reader().FromFile("titanic.csv");
where .Reader() is a convenience method corresponding to:
using var reader = Sep.Auto.Reader().FromFile("titanic.csv");
where Sep? Auto => null; is a static property that returns null for a
nullable Sep to signify that the separator should be inferred from the first
row, which might be a header. If the first row does not contain any of the by
default supported separators or there are no rows, the default separator will be
used.
⚠ Note Sep uses ; as the default separator, since this is what was used in an
internal proprietary library which Sep was built to replace. This is also to
avoid issues with comma , being used as a decimal separator in some locales.
Without having to resort to quoting.
If you want to specify the separator you can write:
using var reader = Sep.New(',').Reader().FromFile("titanic.csv");
or
var sep = new Sep(',');
using var reader = sep.Reader().FromFile("titanic.csv");
Similarly, for SepWriter:
using var writer = Sep.Writer().ToFile("titanic.csv");
or
using var writer = Sep.New(',').Writer().ToFile("titanic.csv");
where you have to specify a valid separator, since it cannot be inferred. To
fascillitate easy flow of the separator and CultureInfo both SepReader and
SepWriter expose a Spec property of type SepSpec that simply defines those
two. This means you can write:
using var reader = Sep.Reader().FromFile("titanic.csv");
using var writer = reader.Spec.Writer().ToFile("titanic-survivors.csv");
where the writer then will use the separator inferred by the reader, for
example.
API Pattern
In general, both reading and writing follow a similar pattern:
where each continuation flows fluently from the preceding type. For example,
Reader() is an extension method to Sep or SepSpec that returns a
SepReaderOptions. Similarly, Writer() is an extension method to Sep or
SepSpec that returns a SepWriterOptions.
SepReaderOptions and
SepWriterOptions are optionally configurable.
That and the APIs for reader and writer is covered in the following sections.
⚠ Note that it is important to understand that Sep Row/Col/Cols are ref structs
(please follow the ref struct link and understand how this limits the usage of
those). This is due to these types being simple facades or indirections to the
underlying reader or writer. That means you cannot use LINQ or create an array
of all rows like reader.ToArray() as the reader is not IEnumerable<> either
since ref structs cannot be used in interfaces, which is in fact the point.
Hence, you need to parse or copy to different types instead. The same applies to
Col/Cols which point to internal state that is also reused. This is to avoid
repeated allocations for each row and get the best possible performance, while
still defining a well structured and straightforward API that guides users to
relevant functionality. See Why SepReader Is Not IEnumerable and LINQ
Compatible for more.
SepReader API
SepReader API has the following structure (in pseudo-C# code):
using var reader = Sep.Reader(o => o).FromFile/FromText/From...;
var header = reader.Header;
var _ = header.IndexOf/IndicesOf/NamesStartingWith...;
foreach (var row in reader)
{
var _ = row[colName/colNames].Span/ToString/Parse<T>...;
var _ = row[colIndex/colIndices].Span/ToString/Parse<T>...;
}
That is, to use SepReader follow the points below:
Optionally define Sep or use default automatically inferred separator.
Specify reader with optional configuration of SepReaderOptions. For
example, if a csv-file does not have a header this can be configured via:
Sep.Reader(o => o with { HasHeader = false })
For all options see SepReaderOptions.
Specify source e.g. file, text (string), TextWriter, etc. via From
extension methods.
Optionally access the header. For example, to get all columns starting with
GT_ use:
var colNames = header.NamesStarting("GT_");
var colIndices = header.IndicesOf(colNames);
Enumerate rows. One row at a time.
Access a column by name or index. Or access multiple columns with names and
indices. Sep internally handles pooled allocation and reuse of arrays for
multiple columns.
Use Span to access the column directly as a ReadOnlySpan<char>. Or use
ToString to convert to a string. Or use Parse<T> where T : ISpanParsable<T> to parse the column chars to a specific type.
SepReaderOptions
The following options are available:
/// <summary>
/// Specifies the separator used, if `null` then automatic detection
/// is used based on first row in source.
/// </summary>
public Sep? Sep { get; init; }
/// <summary>
/// Specifies the culture used for parsing.
/// May be `null` for default culture.
/// </summary>
public CultureInfo? CultureInfo { get; init; }
/// <summary>
/// Indicates whether the first row is a header row.
/// </summary>
public bool HasHeader { get; init; }
/// <summary>
/// Specifies the method factory used to convert a column span
/// of `char`s to a `string`.
/// </summary>
public SepCreateToString CreateToString { get; init; }
/// <summary>
/// Disables using [csFastFloat](https://github.com/CarlVerret/csFastFloat)
/// for parsing `float` and `double`.
/// </summary>
public bool DisableFastFloat { get; init; }
/// <summary>
/// Disables checking if column count is the same for all rows.
/// </summary>
public bool DisableColCountCheck { get; init; }
SepReader Debuggability
Debuggability is an important part of any library and while this is still a work
in progress for Sep, SepReader does have a unique feature when looking at it's
row in a debug context. Given the below example code:
var text = """
Key;Value
A;"1
2
3"
B;"Apple
Banana
Orange
Pear"
""";
using var reader = Sep.Reader().FromText(text);
foreach (var row in reader)
{
// Hover over row when breaking here
if (Debugger.IsAttached && row.RowIndex == 2) { Debugger.Break(); }
}
and you are hovering over row when the break is triggered then this will show
something like:
2:[5..9] = 'B;"Apple\r\nBanana\r\nOrange\r\nPear"
This has the format shown below.
<ROWINDEX>:[<LINENUMBERRANGE>] = '<ROW>'
Note how this shows line number range [FromIncl..ToExcl], as in C# range
expression,
so that one can easily find the row in question in notepad or similar. This
means Sep has to track line endings inside quotes and is an example of a feature
that makes Sep a bit slower but which is a price considered worth paying.
GitHub doesn't show line numbers in code blocks so consider copying the
example text to notepad or similar to see the effect.
Why SepReader Is Not IEnumerable and LINQ Compatible
As mentioned earlier Sep only allows enumeration and access to one row at a time
and SepReader.Row is just a simple facade or indirection to the underlying
reader. This is why it is defined as a ref struct. In fact, the following code:
using var reader = Sep.Reader().FromText(text);
foreach (var row in reader)
{ }
can also be rewritten as:
using var reader = Sep.Reader().FromText(text);
while (reader.MoveNext())
{
var row = reader.Current;
}
where row is just a facade for exposing row specific functionality. That is,
row is still basically the reader underneath. Hence, let's imagine ifSepReader did implement IEnumerable<SepReader.Row> and the Row was not a
ref struct. Then, you would be able to write something like below:
using var reader = Sep.Reader().FromText(text);
SepReader.Row[] rows = reader.ToArray();
Given Row is just a facade for the reader, this would be equivalent to
writing:
using var reader = Sep.Reader().FromText(text);
SepReader[] rows = reader.ToArray();
which hopefully makes it clear why this is not a good thing. The array would
effectively be the reader repeated several times. If this would have to be
supported one would have to allocate memory for each row always, which would
basically be no different than a ReadLine approach as benchmarked in
Comparison Benchmarks.
This is perhaps also the reason why no other efficient .NET CSV parser (known to
author) implements an API pattern like Sep, but instead let the reader define
all functionality directly and hence only let's you access the current row and
cols on that. This API, however, is in this authors opinion not ideal and can be
a bit confusing, which is why Sep is designed like it is. The downside is the
above caveat.
If you want to use LINQ or similar you have to first parse or transform the rows
into some other type and enumerate it. This is easy to do and instead of
counting lines you should focus on how such enumeration can be easily expressed
using C# iterators (aka yield return). With local functions this can be done
inside a method like:
var text = """
Key;Value
A;1.1
B;2.2
""";
var expected = new (string Key, double Value)[] {
("A", 1.1),
("B", 2.2),
};
using var reader = Sep.Reader().FromText(text);
var actual = Enumerate(reader).ToArray();
CollectionAssert.AreEqual(expected, actual);
static IEnumerable<(string Key, double Value)> Enumerate(SepReader reader)
{
foreach (var row in reader)
{
yield return (row["Key"].ToString(), row["Value"].Parse<double>());
}
}
Now if instead refactoring this to something LINQ-compatible by defining a
common Enumerate or similar method it could be:
var text = """
Key;Value
A;1.1
B;2.2
""";
var expected = new (string Key, double Value)[] {
("A", 1.1),
("B", 2.2),
};
using var reader = Sep.Reader().FromText(text);
var actual = Enumerate(reader,
row => (row["Key"].ToString(), row["Value"].Parse<double>()))
.ToArray();
CollectionAssert.AreEqual(expected, actual);
static IEnumerable<T> Enumerate<T>(SepReader reader, SepReader.RowFunc<T> func)
{
foreach (var row in reader)
{
yield return func(row);
}
}
Which discounting the Enumerate method (which could naturally be an extension
method), does have less boilerplate, but not really more effective lines of
code. The issue here is that this tends to favor factoring code in a way that
can become very inefficient quickly. Consider if one wanted to only enumerate
rows matching a predicate on Key which meant only 1% of rows were to be
enumerated e.g.:
var text = """
Key;Value
A;1.1
B;2.2
""";
var expected = new (string Key, double Value)[] {
("B", 2.2),
};
using var reader = Sep.Reader().FromText(text);
var actual = Enumerate(reader,
row => (row["Key"].ToString(), row["Value"].Parse<double>()))
.Where(kv => kv.Item1.StartsWith("B", StringComparison.Ordinal))
.ToArray();
CollectionAssert.AreEqual(expected, actual);
static IEnumerable<T> Enumerate<T>(SepReader reader, SepReader.RowFunc<T> func)
{
foreach (var row in reader)
{
yield return func(row);
}
}
This means you are still parsing the double (which is magnitudes slower than
getting just the key) for all rows. Imagine if this was an array of floating
points or similar. Not only would you then be parsing a lot of values you would
also be allocated 99x arrays that aren't used after filtering with Where.
Instead, you should focus on how to express the enumeration in a way that is
both efficient and easy to read. For example, the above could be rewritten as:
var text = """
Key;Value
A;1.1
B;2.2
""";
var expected = new (string Key, double Value)[] {
("B", 2.2),
};
using var reader = Sep.Reader().FromText(text);
var actual = Enumerate(reader).ToArray();
CollectionAssert.AreEqual(expected, actual);
static IEnumerable<(string Key, double Value)> Enumerate(SepReader reader)
{
foreach (var row in reader)
{
var keyCol = row["Key"];
if (keyCol.Span.StartsWith("B"))
{
yield return (keyCol.ToString(), row["Value"].Parse<double>());
}
}
}
This does not take significantly longer to write and is a lot more efficient
(also avoids allocating a string for key for each row) and is easier to debug
and perhaps even read. All examples above can be seen in
ReadMeTest.cs.
SepWriter API
SepWriter API has the following structure (in pseudo-C# code):
using var writer = Sep.Writer(o => o).ToFile/ToText/To...;
foreach (var data in EnumerateData())
{
using var row = writer.NewRow();
var _ = row[colName/colNames].Set/Format<T>...;
var _ = row[colIndex/colIndices].Set/Format<T>...;
}
That is, to use SepWriter follow the points below:
Optionally define Sep or use default automatically inferred separator.
Specify writer with optional configuration of SepWriterOptions.
For all options see SepWriterOptions.
Specify destination e.g. file, text (string via StringWriter),
TextWriter, etc. via To extension methods.
MISSING: SepWriter currently does not allow you to define the header up
front. Instead, header is defined by the order in which column names are
accessed/created when defining the row.
Define new rows with NewRow. ⚠ Be sure to dispose any new rows before
starting the next! For convenience Sep provides an overload for NewRow that
takes a SepReader.Row and copies the columns from that row to the new row:
using var reader = Sep.Reader().FromText(text);
using var writer = reader.Spec.Writer().ToText();
foreach (var readRow in reader)
{ using var writeRow = writer.NewRow(readRow); }
Create a column by selecting by name or index. Or multiple columns via
indices and names. Sep internally handles pooled allocation and reuse of
arrays for multiple columns.
Use Set to set the column value either as a ReadOnlySpan<char>, string
or via an interpolated string. Or use Format<T> where T : IFormattable
to format T to the column value.
Row is written when Dispose is called on the row.
Note this is to allow a row to be defined flexibly with both column
removal, moves and renames in the future. This is not yet supported.
SepWriterOptions
The following options are available:
/// <summary>
/// Specifies the separator used.
/// </summary>
public Sep Sep { get; init; }
/// <summary>
/// Specifies the culture used for parsing.
/// May be `null` for default culture.
/// </summary>
public CultureInfo? CultureInfo { get; init; }
Limitations and Constraints
Sep is designed to be minimal and fast. As such, it has some limitations and
constraints, since these are not needed for the initial intended usage:
Automatic escaping and unescaping quotes is not supported. Use
Trim
extension method to remove surrounding quotes, for example.
Comments # are not directly supported. You can skip a row by:
foreach (var row in reader)
{
// Skip row if starts with #
if (!row.Span.StartsWith("#"))
{
// ...
}
}
This does not allow skipping a header row starting with # though.
SepWriter is not yet fully featured and one cannot skip writing a header
currently.
Comparison Benchmarks
To investigate the performance of Sep it is compared to:
CsvHelper - the most commonly
used CSV library with a staggering
downloads on NuGet. Fully
featured and battle tested.
ReadLine/WriteLine - basic naive implementations that read line by line
and split on separator. While writing columns, separators and line endings
directly. Does not handle quotes or similar correctly.
All benchmarks are run from/to memory either with:
StringReader or StreamReader + MemoryStream
StringWriter or StreamWriter + MemoryStream
This to avoid confounding factors from reading from or writing to disk.
When using StringReader/StringWriter each char counts as 2 bytes, when
measuring throughput e.g. MB/s. When using StreamReader/StreamWriter
content is UTF-8 encoded and each char typically counts as 1 byte, as content
usually limited to 1 byte per char in UTF-8. Note that in .NET for TextReader
and TextWriter data is converted to/from char, but for reading such
conversion can often be just as fast as Memmove.
By default only StringReader/StringWriter results are shown, if a result is
based on StreamReader/StreamWriter it will be called out. Usually, results
for StreamReader/StreamWriter are in line with StringReader/StringWriter
but with half the throughput due to 1 byte vs 2 bytes. For brevity they are not
shown here.
For all benchmark results, Sep has been defined as the Baseline in
BenchmarkDotNet. This means Ratio will be 1.00
for Sep. For the others Ratio will then show how many times faster Sep is
than that. Or how many times more bytes are allocated in Alloc Ratio.
Disclaimer: Any comparison made is based on a number of preconditions and
assumptions. Sep is a new library written from the ground up to use the latest
and greatest features in .NET. CsvHelper has a long history and has to take
into account backwards compatibility and still supporting older runtimes, so
may not be able to easily utilize more recent features. Same goes for Sylvan.
Additionally, Sep has a different feature set compared to the two. Performance
is a feature, but not the only feature. Keep that in mind when evaluating
results.
Runtime and Platforms
The following runtime is used for benchmarking:
NET 7.0.X
NET 8.0.X
The following platforms are used for benchmarking:
AMD 5950X X64 Platform Information
OS=Windows 10 (10.0.19044.2846/21H2/November2021Update)
AMD Ryzen 9 5950X, 1 CPU, 32 logical and 16 physical cores
Intel Xeon Silver 4316 X64 Platform Information
OS=Windows 10 (10.0.17763.3287/1809/October2018Update/Redstone5)
Intel Xeon Silver 4316 CPU 2.30GHz, 1 CPU, 40 logical and 20 physical cores
Details for each can be found in the following. However, for each of these 3
different scopes are benchmarked to better assertain the low-level performance
of each library and approach and what parts of the parsing consume the most
time:
Row - for this scope only the row is enumerated. That is, for Sep all
that is done is:
foreach (var row in reader) { }
this should capture parsing both row and columns but without accessing these.
Note that some libraries (like Sylvan) will defer work for columns to when
these are accessed.
Cols - for this scope all rows and all columns are enumerated. If
possible columns are accessed as spans, if not as strings, which then might
mean a string has to be allocated. That is, for Sep this is:
foreach (var row in reader)
{
for (var i = 0; i < row.ColCount; i++)
{
var span = row[i].Span;
}
}
XYZ - finally the full scope is performed which is specific to each of
the scenarios.
My goal was to find the fastest low-level CSV parser. Essentially, all I
wanted was a library that gave me a string[] for each line where each field in
the line was an element in the array.
What is great about this work is it tests a whole of 35 different libraries and
approaches to this. Providing a great overview of those and their performance on
this specific scenario. Given Sylvan is the fastest of those it is used as the
one to beat here, while CsvHelper is used to compare to the most commonly used
library.
For Scope = Asset the columns are parsed into a
PackageAsset class, which
consists of 25 properties of which 22 are strings. Each asset is accumulated
into a List<PackageAsset>. Each column is accessed as a string regardless.
This means this benchmark is dominated by turning columns into strings for the
decently fast parsers. Hence, the fastest libraries in this test employ string
pooling. That is, basically a custom dictionary from ReadOnlySpan<char> to
string, which avoids allocating a new string for repeated values. And as can
be seen in the csv-file there are a lot of repeated values. Both Sylvan and
CsvHelper do this in the benchmark. So does Sep and as with Sep this is an
optional configuration that has to be explicitly enable. For Sep this means the
reader is created with something like:
using var reader = Sep.Reader(o => o with
{
HasHeader = false,
CreateToString = SepToString.PoolPerCol(maximumStringLength: 128),
})
.From(CreateReader());
What is unique for Sep is that it allows defining a pool per column e.g. via
SepToString.PoolPerCol(...). This is based on the fact
that often each column has its own set of values or strings that may be repeated
without any overlap to other columns. This also allows one to define per column
specific handling of ToString behavior. Whether to pool or not. Or even to use
a statically defined pool.
PackageAssets Benchmark Results
The results below show Sep is now the fastest .NET CSV Parser (for this
benchmark on these platforms and machines 😀). While for pure parsing allocating
only a fraction of the memory due to extensive use of pooling and the
ArrayPool<T>.
This is in many aspects due to Sep having extremely optimized string pooling and
optimized hashing of ReadOnlySpan<char>, and thus not really due the the
csv-parsing itself, since that is not a big part of the time consumed. At least
not for a decently fast csv-parser.
NCsvPerf does not examine performance in the face of quotes in the csv. This
is relevant since some libraries like Sylvan will revert to a slower (not SIMD
vectorized) parsing code path if it encounters quotes. Sep was designed to
always use SIMD vectorization no matter what.
Since there are two extra chars to handle per column, it does have a
significant impact on performance, no matter what though. This is expected when
looking at the numbers. For each row of 25 columns, there are 24 separators
(here ,) and one set of line endings (here \r\n). That's 26 characters.
Adding quotes around each of the 25 columns will add 50 characters or almost
triple the total to 76.
The FloatsReaderBench.cs
benchmark demonstrates what Sep is built for. Namely parsing 32-bit floating
points or features as in machine learning. Here a simple CSV-file is randomly
generated with N ground truth values, N predicted result values and some
typical extra columns leading that, but which aren't used as such in the
benchmark. N = 20 here. For example:
For Scope=Floats the benchmark will parse the features as two spans of
floats; one for ground truth values and one for predicted result values. Then
calculates the mean squared error (MSE) of those as an example. For Sep this
code is succinct and still incredibly efficient:
using var reader = Sep.Reader().From(Reader.CreateReader());
var groundTruthColNames = reader.Header.NamesStartingWith("GT_");
var resultColNames = groundTruthColNames.Select(n =>
n.Replace("GT_", "RE_", StringComparison.Ordinal))
.ToArray();
var sum = 0.0;
var count = 0;
foreach (var row in reader)
{
var gts = row[groundTruthColNames].Parse<float>();
var res = row[resultColNames].Parse<float>();
sum += MeanSquaredError(gts, res);
++count;
}
return sum / count;
Note how one can access and parse multiple columns easily while there are no
repeated allocations for the parsed floating points. Sep internally handles a
pool of arrays for handling multiple columns and returns spans for them.
The benchmark is based on an assumption of accessing columns by name per
row. Ideally, one would look up the indices of the columns by name before
enumerating rows, but this is a repeated nuisance to have to handle and Sep was
built to avoid this. Hence, the comparison is based on looking up by name for
each, even if this ends up adding a bit more code in the benchmark for other
approaches.
As can be seen below, the actual low level parsing of the separated values is a
tiny part of the total runtime for Sep for which the run time is dominated by
parsing the floating points. Since Sep uses
csFastFloat for an integrated fast
floating point parser, it is >2x faster than Sylvan for example. If using
Sylvan one may consider using csFastFloat if that is an option.
CsvHelper suffers from the fact that one can only access the column as a string
so this has to be allocated for each column (ReadLine by definition always
allocates a string per column). Still CsvHelper is significantly slower than the
naive ReadLine approach. With Sep being >3.8x faster than CsvHelper.
It is a testament to how good the .NET and the .NET GC is that the ReadLine is
pretty good compared to CsvHelper regardless of allocating a lot of strings.
Writer benchmarks are still pending, but Sep is unlikely to be the fastest here
since it is explicitly designed to make writing more convenient and flexible.
Still efficient, but not necessarily fastest. That is, Sep does not require
writing header up front and hence having to keep header column order and row
values column order the same. This means Sep does not write columns directly
upon definition but defers this until a new row has been fully defined and then
is ended.
Example Catalogue
The following examples are available in ReadMeTest.cs.
Example - Copy Rows
var text = """
A;B;C;D;E;F
Sep;🚀;1;1.2;0.1;0.5
CSV;✅;2;2.2;0.2;1.5
"""; // Empty line at end is for line ending
using var reader = Sep.Reader().FromText(text);
using var writer = reader.Spec.Writer().ToText();
foreach (var readRow in reader)
{
using var writeRow = writer.NewRow(readRow);
}
Assert.AreEqual(text, writer.ToString());
RFC-4180
While the RFC-4180 requires \r\n
(CR,LF) as line ending, the well-known line endings (\r\n, \n and \r) are
supported similar to .NET. Environment.NewLine is used when writing. Quoting
is supported by simply matching pairs of quotes, no matter what. With no
automatic escaping. Hence, you are responsible and in control of this at this
time.
Note that some libraries will claim conformance but the RFC is, perhaps
naturally, quite strict e.g. only comma is supported as separator/delimiter. Sep
defaults to using ; as separator if writing, while auto-detecting supported
separators when reading. This is decidedly non-conforming.
The RFC defines the following condensed ABNF
grammar:
file = [header CRLF] record *(CRLF record) [CRLF]
header = name *(COMMA name)
record = field *(COMMA field)
name = field
field = (escaped / non-escaped)
escaped = DQUOTE *(TEXTDATA / COMMA / CR / LF / 2DQUOTE) DQUOTE
non-escaped = *TEXTDATA
COMMA = %x2C
CR = %x0D ;as per section 6.1 of RFC 2234 [2]
DQUOTE = %x22 ;as per section 6.1 of RFC 2234 [2]
LF = %x0A ;as per section 6.1 of RFC 2234 [2]
CRLF = CR LF ;as per section 6.1 of RFC 2234 [2]
TEXTDATA = %x20-21 / %x23-2B / %x2D-7E
Note how TEXTDATA is restricted too, yet many will allow any character incl.
emojis or similar (which Sep supports), but is not in conformance with the RFC.
Quotes inside an escaped field e.g. "fie""ld" are only allowed to be double
quotes. Sep currently allows any pairs of quotes and quoting doesn't need to be
at start of or end of field (col or column in Sep terminology).
All in all Sep takes a pretty pragmatic approach here as the primary use case is
not exchanging data on the internet, but for use in machine learning
pipelines or similar.
Frequently Asked Questions (FAQ)
Ask questions on GitHub and this section will be expanded. :)
downloads on NuGet. Fully
featured and battle tested.