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https://github.com/cemderv/linq
A header-only LINQ library for C++
https://github.com/cemderv/linq
cpp linq modern-cpp ranges
Last synced: 14 days ago
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A header-only LINQ library for C++
- Host: GitHub
- URL: https://github.com/cemderv/linq
- Owner: cemderv
- License: apache-2.0
- Created: 2024-09-20T17:31:08.000Z (3 months ago)
- Default Branch: main
- Last Pushed: 2024-10-01T17:43:47.000Z (3 months ago)
- Last Synced: 2024-10-17T22:56:44.630Z (3 months ago)
- Topics: cpp, linq, modern-cpp, ranges
- Language: C++
- Homepage:
- Size: 96.7 KB
- Stars: 1
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# linq - LINQ for C++
linq is a header-only LINQ library for C++ 17 and newer.
It has no dependencies and neatly integrates into the STL by taking advantage of modern C++ features.
linq ...
- resolves all type-related functionality at compile-time; no virtual dispatch is used
- uses lazy evaluation, so your queries still work even after you modify the container it's based on
- focuses on immutability, so your queries stay predictable
- is efficient in the way it works with your data; it avoids copies and instead moves data wherever it can
- generates an operation chain at compile-time
- works with all generic container types, not just the STL
- does not rely on exceptions and instead reports errors at compile-time
- uses the beloved dot operator!
---
linq has been tested with the following compilers:
- Clang 16+
- GCC 10+
- AppleClang 13+
- MSVC 2019+
[](https://github.com/cemderv/linq/actions/workflows/build-linux-clang.yml) [](https://github.com/cemderv/linq/actions/workflows/build-linux-gcc.yml) [](https://github.com/cemderv/linq/actions/workflows/build-macos-appleclang.yml) [](https://github.com/cemderv/linq/actions/workflows/build-windows-msvc.yml)
## Examples
#### Intro
```cpp
#include
struct Person {
string name;
int age;
};
const vector people {
{ .name = "P1", .age = 20 },
{ .name = "P2", .age = 21 },
{ .name = "P3", .age = 22 },
};
auto query = linq::from(&people)
.where( [](const Person& p) { return p.age > 20; } );
for (const Person& p : query) {
println("{}, {}", p.name, p.age);
}
```
Output:
```
P2, 21
P3, 22
```
#### Aggregation
```cpp
double average_age = linq::from(&people)
.select( [](const Person& p) { return p.age; } )
.average();
int people_over_20 = linq::from(&people)
.where( [](const Person& p) { return p.age > 20; } )
.count();
```
#### Element access
```cpp
const auto over_20 = [](const Person& p) { return p.age > 20; };
const auto under_20 = [](const Person& p) { return p.age < 20; };
optional first_over_20 = linq::from(&people).first(over_20);
// first_over_20 = P2, 21
optional last_over_20 = linq::from(&people).last(over_20);
// last_over_20 = P3, 22
optional first_under_20 = linq::from(&people).last(under_20);
// first_under_20 = empty optional
```
#### Partitioning
```cpp
const vector numbers { 1, 2, 3, 4, 5, 6 };
auto query1 = linq::from(&numbers).skip(3); // 4, 5, 6
auto query2 = linq::from(&numbers)
.skip_while( [](int i) { return i < 4; } ); // 4, 5, 6
auto query3 = linq::from(&numbers).take(4); // 1, 2, 3, 4
auto query4 = linq::from(&numbers)
.take_while( [](int i) { return i < 4; } ); // 1, 2, 3
```
#### Sorting
```cpp
const vector words { "hello"s, "world"s, "here"s, "are"s, "some"s, "sorted"s, "words"s };
auto query = linq::from(&words)
.order_by_ascending( [](const string& word) { return word.size(); } )
.then_by_ascending( [](const string& word) { return word; } );
// query = are, here, some, hello, words, world, sorted
auto rev = query.reverse();
// rev = sorted, world, words, hello, some, here, are
```
#### Concatenation
```cpp
const vector numbers1 { 1, 2, 3 };
const vector numbers2 { 4, 5, 6 };
auto range = linq::from(&numbers1)
.append(linq::from(&numbers2));
// range = 1, 2, 3, 4, 5, 6
```
#### Removing duplicates
```cpp
const vector numbers { 1, 2, 3, 3, 5, 4, 5, 6, 7 };
const auto query = linq::from(&numbers).distinct();
// query = 1, 2, 3, 5, 4, 6, 7
```
#### Composition
```cpp
auto people = linq::from(&people);
auto age_over_20 = [](const Person& p) { return p.age > 20; };
auto people_over_20 = people.where(age_over_20);
auto person_age = [](const Person& p) { return p.age; };
double average_age = people_over_20.select(person_age).average();
```
#### Producing containers
`to_vector`:
```cpp
const array numbers { 1, 2, 3, 4 };
vector vec = linq::from(&numbers)
.where( [](int i) { return i > 1; } )
.select_to_string()
.to_vector(); // copy elements to a new std::vector
// 'vec' is of type std::vector
// with contents ["2", "3", "4"]
```
`to_map`:
```cpp
const array pairs {
pair{ 1, "str1"s },
pair{ 5, "str5"s },
pair{ -10, "str-10"s },
};
const auto query = linq::from(&pairs)
.where( [](const auto& p) { return p.first < 20; } );
map my_map = query.to_map();
for (const auto& [key, value] : my_map) {
println("[{}: {}]", key, value);
}
```
Output:
```
[-10: str-10]
[1: str1]
[5: str5]
```
### Generation
```cpp
auto range1 = linq::from_to(0, 5); // 0, 1, 2, 3, 4, 5
auto range2 = linq::from_to(0.0, 1.5, 0.5); // 0, 0.5, 1, 1.5
auto range3 = linq::from_to(0, 3).repeat(1); // 0, 1, 2, 3, 0, 1, 2, 3
auto range4 = linq::generate([](size_t i) {
if (i < 5)
return linq::generate_return(i * 2);
return linq::generate_finish();
});
// range4 = 0, 2, 4, 6, 8
```
---
Below you will find a list of all supported functions and operators.
### Query Constructors
- [from](https://github.com/cemderv/linq/wiki/Query-Constructors#from)
- [from_mutable](https://github.com/cemderv/linq/wiki/Query-Constructors#from_mutable)
- [from_copy](https://github.com/cemderv/linq/wiki/Query-Constructors#from_copy)
### Container Producers
- [to_vector](https://github.com/cemderv/linq/wiki/Container-Producers#to_vector)
- [to_map / to_unordered_map](https://github.com/cemderv/linq/wiki/Container-Producers#to_map--to_unordered_map)
### Operators
- [Aggregation](https://github.com/cemderv/linq/wiki/Aggregate-Operators)
- [aggregate](https://github.com/cemderv/linq/wiki/Aggregate-Operators#aggregate)
- [average](https://github.com/cemderv/linq/wiki/Aggregate-Operators#average)
- [count](https://github.com/cemderv/linq/wiki/Aggregate-Operators#count)
- [max](https://github.com/cemderv/linq/wiki/Aggregate-Operators#max)
- [min](https://github.com/cemderv/linq/wiki/Aggregate-Operators#min)
- [sum](https://github.com/cemderv/linq/wiki/Aggregate-Operators#sum)
- [Concatenation](https://github.com/cemderv/linq/wiki/Concatenation-Operators)
- [append](https://github.com/cemderv/linq/wiki/Concatenation-Operators#append)
- [Element Access](https://github.com/cemderv/linq/wiki/Element-Operators)
- [element_at](https://github.com/cemderv/linq/wiki/Element-Operators#element_at)
- [first](https://github.com/cemderv/linq/wiki/Element-Operators#first)
- [last](https://github.com/cemderv/linq/wiki/Element-Operators#last)
- [Filters](https://github.com/cemderv/linq/wiki/Filter-Operators)
- [where](https://github.com/cemderv/linq/wiki/Filter-Operators#where)
- [Generation](https://github.com/cemderv/linq/wiki/Generation-Operators)
- [from_to](https://github.com/cemderv/linq/wiki/Generation-Operators#from_to)
- [repeat](https://github.com/cemderv/linq/wiki/Generation-Operators#repeat)
- [generate](https://github.com/cemderv/linq/wiki/Generation-Operators#generate)
- [Join](https://github.com/cemderv/linq/wiki/Join-Operators)
- [join](https://github.com/cemderv/linq/wiki/Join-Operators#join)
- [Partition](https://github.com/cemderv/linq/wiki/Partition-Operators)
- [skip](https://github.com/cemderv/linq/wiki/Partition-Operators#skip)
- [skip_while](https://github.com/cemderv/linq/wiki/Partition-Operators#skip_while)
- [take](https://github.com/cemderv/linq/wiki/Partition-Operators#take)
- [take_while](https://github.com/cemderv/linq/wiki/Partition-Operators#take_while)
- [Projection](https://github.com/cemderv/linq/wiki/Projection-Operators)
- [select](https://github.com/cemderv/linq/wiki/Projection-Operators#select)
- [select_to_string](https://github.com/cemderv/linq/wiki/Projection-Operators#select_to_string)
- [select_many](https://github.com/cemderv/linq/wiki/Projection-Operators#select_many)
- [Quantifiers](https://github.com/cemderv/linq/wiki/Quantifier-Operators)
- [all](https://github.com/cemderv/linq/wiki/Quantifier-Operators#all)
- [any](https://github.com/cemderv/linq/wiki/Quantifier-Operators#any)
- [Set](https://github.com/cemderv/linq/wiki/Set-Operators)
- [distinct](https://github.com/cemderv/linq/wiki/Set-Operators#distinct)
- [Sorting](https://github.com/cemderv/linq/wiki/Sorting-Operators)
- [order_by](https://github.com/cemderv/linq/wiki/Sorting-Operators#order_by)
- [then_by](https://github.com/cemderv/linq/wiki/Sorting-Operators#then_by)
- [reverse](https://github.com/cemderv/linq/wiki/Sorting-Operators#reverse)