README.md · 吉良吉影/MoreLINQ

# MoreLINQ

LINQ to Objects is missing a few desirable features.

This project enhances LINQ to Objects with extra methods, in a manner which
keeps to the spirit of LINQ.

MoreLINQ is available for download and installation as
[NuGet packages](https://www.nuget.org/packages/morelinq/).

Documentation for the stable and beta releases can be found at
[morelinq.github.io](https://morelinq.github.io/).

## Usage

MoreLINQ can be used in one of two ways. The simplest is to just import the
`MoreLinq` namespace and all extension methods become instantly available for
you to use on the types they extend (typically some instantiation of
`IEnumerable<T>`). In some very rare instances, however, doing so can cause
conflicts with other libraries you may be using that incidentally also extend
the same type with an identically named method and signature. This happened
with MoreLINQ, for example, when Microsoft .NET Framework 4.0 introduced
[`Zip`][netzip] and [MoreLINQ already had one][zip]. Starting with version 3.0
of MoreLINQ, you can reduce the potential for present (or even future)
conflicts by individually importing just the extension methods you need using
the [static imports feature introduced in C# 6][using-static]:

```c#
using static MoreLinq.Extensions.LagExtension;
using static MoreLinq.Extensions.LeadExtension;
```

In the example above, only the [`Lag`][lag] and [`Lead`][lead] extension
methods will be available in scope.

Apart from extension methods, MoreLINQ also offers regular static method that
*generate* (instead of operating on) sequences, like [`Unfold`][unfold],
[`Random`][random], [`Sequence`][sequence] and others. If you want to use these
while statically importing other individual extension methods, you can do so via
aliasing:

```c#
using static MoreLinq.Extensions.LagExtension;
using static MoreLinq.Extensions.LeadExtension;
using MoreEnumerable = MoreLinq.MoreEnumerable;
```

In the example above, [`Lag`][lag] and [`Lead`][lead] will be available as
extension methods as well as all the regular static methods on
`MoreEnumerable` but _without_ any of the extension methods offered by
`MoreEnumerable`.

[lag]: https://morelinq.github.io/2.0/ref/api/html/Overload_MoreLinq_MoreEnumerable_Lag.htm
[lead]: https://morelinq.github.io/2.0/ref/api/html/Overload_MoreLinq_MoreEnumerable_Lead.htm
[using-static]: https://docs.microsoft.com/en-us/dotnet/articles/csharp/whats-new/csharp-6#using-static
[netzip]: https://docs.microsoft.com/en-us/dotnet/api/system.linq.enumerable.zip#System_Linq_Enumerable_Zip__3_System_Collections_Generic_IEnumerable___0__System_Collections_Generic_IEnumerable___1__System_Func___0___1___2__
[zip]: https://morelinq.github.io/1.x/ref/api/html/M_MoreLinq_MoreEnumerable_Zip__3.htm
[unfold]: https://morelinq.github.io/2.3/ref/api/html/M_MoreLinq_MoreEnumerable_Unfold__3.htm
[random]: https://morelinq.github.io/2.0/ref/api/html/Overload_MoreLinq_MoreEnumerable_Random.htm
[sequence]: https://morelinq.github.io/2.2/ref/api/html/Overload_MoreLinq_MoreEnumerable_Sequence.htm

## Building

Run either `build.cmd` if building on Windows or `build.sh` if building on macOS
or a [Linux distribution supported by .NET][dotnet-linux].

Some code in the project is generated using [T4][t4] templates. To regenerate
the code from modified templates, run `MoreLinq\tt.cmd` (Windows) or
`MoreLinq/tt.sh` depending on your platform.

Building the documentation is supported on Windows only and requires
[Sandcastle Help File Builder (SHFB)][shfb]. Executing `builddocs.cmd`
generates the documentation in the `docs/api` directory. It can be browsed
locally using any HTTP server of static files, like
[dotnet-serve][dotnet-serve].

[dotnet-linux]: https://learn.microsoft.com/en-us/dotnet/core/install/linux
[shfb]: https://github.com/EWSoftware/SHFB/releases/tag/v2022.12.30.0
[dotnet-serve]: https://www.nuget.org/packages/dotnet-serve
[t4]: https://docs.microsoft.com/en-us/visualstudio/modeling/code-generation-and-t4-text-templates

### Dev Container

For a consistent development experience, you can use [Visual Studio Code] with
the [Dev Containers extension]. A [dev container] provides a ready-to-use
development environment with all the necessary dependencies.

[Visual Studio Code]: https://code.visualstudio.com/
[Dev Containers extension]: https://marketplace.visualstudio.com/items?itemName=ms-vscode-remote.remote-containers
[dev container]: .devcontainer/README.md

## Operators

### Acquire

Ensures that a source sequence of disposable objects are all acquired
successfully. If the acquisition of any one fails then those successfully
acquired till that point are disposed.

### Aggregate

Applies multiple accumulators sequentially in a single pass over a sequence.

This method has 7 overloads.

### AggregateRight

Applies a right-associative accumulator function over a sequence.
This operator is the right-associative version of the Aggregate LINQ operator.

This method has 3 overloads.

### Append

Returns a sequence consisting of the head element and the given tail elements.

### Assert

Asserts that all elements of a sequence meet a given condition otherwise
throws an exception.

This method has 2 overloads.

### AssertCount

Asserts that a source sequence contains a given count of elements.

This method has 2 overloads.

### AtLeast

Determines whether or not the number of elements in the sequence is greater
than or equal to the given integer.

### AtMost

Determines whether or not the number of elements in the sequence is lesser
than or equal to the given integer.

### Backsert

Inserts the elements of a sequence into another sequence at a
specified index from the tail of the sequence, where zero always represents
the last position, one represents the second-last element, two represents
the third-last element and so on.

### Batch

Batches the source sequence into sized buckets.

This method has 4 overloads, 2 of which are experimental.

### Cartesian

Returns the Cartesian product of two or more sequences by combining each
element from the sequences and applying a user-defined projection to the
set.

This method has 7 overloads.

### Choose

Applies a function to each element of the source sequence and returns a new
sequence of result elements for source elements where the function returns a
couple (2-tuple) having a `true` as its first element and result as the
second.

### CompareCount

Compares two sequences and returns an integer that indicates whether the
first sequence has fewer, the same or more elements than the second sequence.

### ~~Concat~~

Returns a sequence consisting of the head element and the given tail elements.

This extension was rendered obsolete in version 3.0 and eventually removed in
version 4.0. Use [`Append`][linq-append] from .NET instead that's been available
since .NET Standard 1.6+, .NET Core 1.0+ and .NET Framework 4.7.1+.

[linq-append]: https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.append

### Consume

Completely consumes the given sequence. This method uses immediate execution,
and doesn't store any data during execution

### CountBetween

Determines whether or not the number of elements in the sequence is between an
inclusive range of minimum and maximum integers.

### CountBy

Applies a key-generating function to each element of a sequence and returns a
sequence of unique keys and their number of occurrences in the original
sequence.

This method has 2 overloads.

### CountDown

Provides a countdown counter for a given count of elements at the tail of the
sequence where zero always represents the last element, one represents the
second-last element, two represents the third-last element and so on.

### DistinctBy

Returns all distinct elements of the given source, where "distinctness" is
determined via a projection and the default equality comparer for the
projected type.

This method has 2 overloads.

### Duplicates

Returns all duplicate elements of the given source.

This method has 2 overloads.

### EndsWith

Determines whether the end of the first sequence is equivalent to the second
sequence.

This method has 2 overloads.

### EquiZip

Returns a projection of tuples, where each tuple contains the N-th
element from each of the argument sequences. An exception is thrown
if the input sequences are of different lengths.

This method has 3 overloads.

### Exactly

Determines whether or not the number of elements in the sequence is equals
to the given integer.

### ExceptBy

Returns the set of elements in the first sequence which aren't in the second
sequence, according to a given key selector.

This method has 2 overloads.

### Exclude

Excludes elements from a sequence starting at a given index

### FallbackIfEmpty

Returns the elements of a sequence and falls back to another if the original
sequence is empty.

This method has 6 overloads.

### FillBackward

Returns a sequence with each null reference or value in the source replaced
with the following non-null reference or value in that sequence.

This method has 3 overloads.

### FillForward

Returns a sequence with each null reference or value in the source replaced
with the previous non-null reference or value seen in that sequence.

This method has 3 overloads.

### Flatten

Flattens a sequence containing arbitrarily-nested sequences.

This method has 3 overloads.

### Fold

Returns the result of applying a function to a sequence with 1 to 16 elements.

This method has 16 overloads.

### ForEach

Immediately executes the given action on each element in the source sequence.

This method has 2 overloads.

### From

Returns a sequence containing the values resulting from invoking (in order)
each function in the source sequence of functions.

This method has 4 overloads.

### FullGroupJoin

Performs a Full Group Join between the and sequences.

This method has 4 overloads.

### FullJoin

Performs a full outer join between two sequences.

This method has 4 overloads.

### Generate

Returns a sequence of values consecutively generated by a generator function

### GenerateByIndex

Returns a sequence of values based on indexes

### GroupAdjacent

Groups the adjacent elements of a sequence according to a specified key
selector function.

This method has 6 overloads.

### ~~Incremental~~

`Incremental` was redundant with `Pairwise` and so deprecated since version
[2.1][v2.1]. It was eventually removed in version [3.0][v3.0].

### Index

Returns a sequence of where the key is the zero-based index of the value in
the source sequence.

This method has 2 overloads.

### IndexBy

Applies a key-generating function to each element of a sequence and returns
a sequence that contains the elements of the original sequence as well its
key and index inside the group of its key. An additional argument specifies
a comparer to use for testing equivalence of keys.

This method has 2 overloads.

### Insert

Inserts the elements of a sequence into another sequence at a specified index.

### Interleave

Interleaves the elements of two or more sequences into a single sequence,
skipping sequences as they are consumed.

### Lag

Produces a projection of a sequence by evaluating pairs of elements separated
by a negative offset.

This method has 2 overloads.

### Lead

Produces a projection of a sequence by evaluating pairs of elements separated
by a positive offset.

This method has 2 overloads.

### LeftJoin

Performs a left outer join between two sequences.

This method has 4 overloads.

### ~~MaxBy~~

:warning: **This method is obsolete. Use [`Maxima`](#maxima) instead.**

Returns the maxima (maximal elements) of the given sequence, based on the
given projection.

This method has 2 overloads.

### Maxima

Returns the maxima (maximal elements) of the given sequence, based on the
given projection.

This method has 2 overloads.

### ~~MinBy~~

:warning: **This method is obsolete. Use [`Minima`](#minima) instead.**

Returns the minima (minimal elements) of the given sequence, based on the
given projection.

This method has 2 overloads.

### Minima

Returns the minima (minimal elements) of the given sequence, based on the
given projection.

This method has 2 overloads.

### Move

Returns a sequence with a range of elements in the source sequence
moved to a new offset.

### OrderBy

Sorts the elements of a sequence in a particular direction (ascending,
descending) according to a key.

This method has 2 overloads.

### OrderedMerge

Merges two ordered sequences into one. Where the elements equal in both
sequences, the element from the first sequence is returned in the resulting
sequence.

This method has 7 overloads.

### Pad

Pads a sequence with default values if it is narrower (shorter in length) than
a given width.

This method has 3 overloads.

### PadStart

Pads a sequence with default values in the beginning if it is narrower
(shorter in length) than a given width.

This method has 3 overloads.

### Pairwise

Returns a sequence resulting from applying a function to each element in the
source sequence and its predecessor, with the exception of the first element
which is only returned as the predecessor of the second element

### PartialSort

Combines `OrderBy` (where element is key) and `Take` in a single operation.

This method has 4 overloads.

### PartialSortBy

Combines `OrderBy` and `Take` in a single operation.

This method has 4 overloads.

### Partition

Partitions a sequence by a predicate, or a grouping by Boolean keys or up to 3
sets of keys.

This method has 10 overloads.

### Permutations

Generates a sequence of lists that represent the permutations of the original
sequence

### Pipe

Executes the given action on each element in the source sequence and yields it

### Prepend

Prepends a single value to a sequence

### PreScan

Performs a pre-scan (exclusive prefix sum) on a sequence of elements

### Random

Returns an infinite sequence of random integers using the standard .NET random
number generator.

This method has 6 overloads.

### RandomDouble

Returns an infinite sequence of random double values between 0.0 and 1.0.

This method has 2 overloads.

### RandomSubset

Returns a sequence of a specified size of random elements from the original
sequence.

This method has 2 overloads.

### Rank

Ranks each item in the sequence in descending ordering using a default
comparer.

This method has 2 overloads.

### RankBy

Ranks each item in the sequence in descending ordering by a specified key
using a default comparer.

This method has 2 overloads.

### Repeat

Repeats the sequence indefinitely or a specific number of times.

This method has 2 overloads.

### Return

Returns a single-element sequence containing the item provided.

### RightJoin

Performs a right outer join between two sequences.

This method has 4 overloads.

### RunLengthEncode

Run-length encodes a sequence by converting consecutive instances of the same
element into a `KeyValuePair<T, int>` representing the item and its occurrence
count.

This method has 2 overloads.

### Scan

Peforms a scan (inclusive prefix sum) on a sequence of elements.

This method has 2 overloads.

### ScanBy

Applies an accumulator function over sequence element keys, returning the keys
along with intermediate accumulator states.

This method has 2 overloads.

### ScanRight

Peforms a right-associative scan (inclusive prefix) on a sequence of elements.
This operator is the right-associative version of the Scan operator.

This method has 2 overloads.

### Segment

Divides a sequence into multiple sequences by using a segment detector based
on the original sequence.

This method has 3 overloads.

### Sequence

Generates a sequence of [numbers] within the (inclusive) specified range.

This method has 5 overloads.

[numbers]: https://learn.microsoft.com/en-us/dotnet/api/system.numerics.inumber-1

### Shuffle

Returns a sequence of elements in random order from the original sequence.

This method has 2 overloads.

### SkipLast

Bypasses a specified number of elements at the end of the sequence.

### SkipLastWhile

Removes elements from the end of a sequence as long as a specified condition is true.

### SkipUntil

Skips items from the input sequence until the given predicate returns true
when applied to the current source item; that item will be the last skipped

### Slice

Extracts elements from a sequence at a particular zero-based starting index

### SortedMerge

Merges two or more sequences that are in a common order (either ascending or
descending) into a single sequence that preserves that order.

This method has 2 overloads.

### Split

Splits the source sequence by a separator.

This method has 12 overloads.

### StartsWith

Determines whether the beginning of the first sequence is equivalent to the
second sequence.

This method has 2 overloads.

### Subsets

Returns a sequence of representing all of the subsets of any size that are
part of the original sequence.

This method has 2 overloads.

### TagFirstLast

Returns a sequence resulting from applying a function to each element in the
source sequence with additional parameters indicating whether the element is
the first and/or last of the sequence

### TakeEvery

Returns every N-th element of a source sequence

### TakeLast

Returns a specified number of contiguous elements from the end of a sequence

### TakeUntil

Returns items from the input sequence until the given predicate returns true
when applied to the current source item; that item will be the last returned

### ThenBy

Performs a subsequent ordering of elements in a sequence in a particular
direction (ascending, descending) according to a key.

This method has 2 overloads.

### ToArrayByIndex

Creates an array from an IEnumerable<T> where a function is used to determine
the index at which an element will be placed in the array.

This method has 6 overloads.

### ToDataTable

Appends elements in the sequence as rows of a given object with a set of
lambda expressions specifying which members (property or field) of each
element in the sequence will supply the column values.

This method has 4 overloads.

### ToDelimitedString

Creates a delimited string from a sequence of values. The delimiter used
depends on the current culture of the executing thread.

This method has 15 overloads.

### ToDictionary

Creates a [dictionary][dict] from a sequence of [key-value pair][kvp] elements
or tuples of 2.

This method has 4 overloads.

### ToHashSet

Returns a [hash-set][hashset] of the source items using the default equality
comparer for the type.

This method has 2 overloads.

### ToLookup

Creates a [lookup][lookup] from a sequence of [key-value pair][kvp] elements
or tuples of 2.

This method has 4 overloads.

### Transpose

Transposes the rows of a sequence into columns.

### TraverseBreadthFirst

Traverses a tree in a breadth-first fashion, starting at a root node and using
a user-defined function to get the children at each node of the tree.

### TraverseDepthFirst

Traverses a tree in a depth-first fashion, starting at a root node and using a
user-defined function to get the children at each node of the tree.

### Trace

Traces the elements of a source sequence for diagnostics.

This method has 3 overloads.

### Unfold

Returns a sequence generated by applying a state to the generator function,
and from its result, determines if the sequence should have a next element and
its value, and the next state in the recursive call.

### Window

Processes a sequence into a series of subsequences representing a windowed
subset of the original

### ~~Windowed~~

Processes a sequence into a series of subsequences representing a windowed
subset of the original

This method was removed and has been superseded by [`Window`](#window) instead.

### WindowLeft

Creates a left-aligned sliding window over the source sequence of a given size.

### WindowRight

Creates a right-aligned sliding window over the source sequence of a given size.

### ZipLongest

Returns a projection of tuples, where each tuple contains the N-th
element from each of the argument sequences. The resulting sequence
will always be as long as the longest of input sequences where the
default value of each of the shorter sequence element types is used
for padding.

This method has 3 overloads.

### ZipShortest

Returns a projection of tuples, where each tuple contains the N-th
element from each of the argument sequences. The resulting sequence
is as short as the shortest input sequence.

This method has 3 overloads.

## Experimental Operators

THESE METHODS ARE EXPERIMENTAL. THEY MAY BE UNSTABLE AND UNTESTED. THEY MAY BE
REMOVED FROM A FUTURE MAJOR OR MINOR RELEASE AND POSSIBLY WITHOUT NOTICE. USE
THEM AT YOUR OWN RISK. THE METHODS ARE PUBLISHED FOR FIELD EXPERIMENTATION TO
SOLICIT FEEDBACK ON THEIR UTILITY AND DESIGN/IMPLEMENTATION DEFECTS.

Use of experimental methods requires importing the `MoreLinq.Experimental`
namespace.

### Aggregate

Applies multiple accumulator queries sequentially in a single pass over a
sequence.

This method has 8 overloads.

### Await

Creates a sequence query that streams the result of each task in the source
sequence as it completes asynchronously.

This method has 2 overloads.

### AwaitCompletion

Awaits completion of all asynchronous evaluations irrespective of whether they
succeed or fail. An additional argument specifies a function that projects the
final result given the source item and completed task.

### Memoize

Creates a sequence that lazily caches the source as it is iterated for the
first time, reusing the cache thereafter for future re-iterations. If the
source is already cached or buffered then it is returned verbatim.

### Merge

Concurrently merges all the elements of multiple asynchronous streams into a
single asynchronous stream. An overload with an additional parameter specifies
the maximum concurrent operations that may be in flight at any give time.

This method has 2 overloads.

### TrySingle

Returns the only element of a sequence that has just one element. If the
sequence has zero or multiple elements, then returns a user-defined value
that indicates the cardinality of the result sequence.

This method has 2 overloads.

[#122]: https://github.com/morelinq/MoreLINQ/issues/122
[dict]: https://docs.microsoft.com/en-us/dotnet/api/System.Collections.Generic.Dictionary-2
[hashset]: https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.hashset-1
[kvp]: https://docs.microsoft.com/en-us/dotnet/api/System.Collections.Generic.KeyValuePair-2
[lookup]: https://docs.microsoft.com/en-us/dotnet/api/system.linq.lookup-2
[v2.1]: https://github.com/morelinq/MoreLINQ/releases/tag/v2.1.0
[v3.0]: https://github.com/morelinq/MoreLINQ/releases/tag/v3.0.0

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