go-linq 
A powerful language integrated query (LINQ) library for Go.
- Written in vanilla Go, no dependencies!
- Complete lazy evaluation with iterator pattern
- Safe for concurrent use
- Supports generic functions to make your code cleaner and free of type assertions
- Supports arrays, slices, maps, strings, channels and custom collections
Installation
When used with Go modules, use the following import path:
go get github.com/ahmetb/go-linq/v3
Older versions of Go using different dependency management tools can use the following import path to prevent breaking API changes:
go get gopkg.in/ahmetb/go-linq.v3
Quickstart
Usage is as easy as chaining methods like:
From(slice) .Where(predicate) .Select(selector) .Union(data)
Example 1: Find all owners of cars manufactured after 2015
import . "github.com/ahmetb/go-linq/v3"
type Car struct {
year int
owner, model string
}
...
var owners []string
From(cars).Where(func(c interface{}) bool {
return c.(Car).year >= 2015
}).Select(func(c interface{}) interface{} {
return c.(Car).owner
}).ToSlice(&owners)
Or, you can use generic functions, like WhereT and SelectT to simplify your code (at a performance penalty):
var owners []string
From(cars).WhereT(func(c Car) bool {
return c.year >= 2015
}).SelectT(func(c Car) string {
return c.owner
}).ToSlice(&owners)
Example 2: Find the author who has written the most books
import . "github.com/ahmetb/go-linq/v3"
type Book struct {
id int
title string
authors []string
}
author := From(books).SelectMany( // make a flat array of authors
func(book interface{}) Query {
return From(book.(Book).authors)
}).GroupBy( // group by author
func(author interface{}) interface{} {
return author // author as key
}, func(author interface{}) interface{} {
return author // author as value
}).OrderByDescending( // sort groups by its length
func(group interface{}) interface{} {
return len(group.(Group).Group)
}).Select( // get authors out of groups
func(group interface{}) interface{} {
return group.(Group).Key
}).First() // take the first author
Example 3: Implement a custom method that leaves only values greater than the specified threshold
type MyQuery Query
func (q MyQuery) GreaterThan(threshold int) Query {
return Query{
Iterate: func() Iterator {
next := q.Iterate()
return func() (item interface{}, ok bool) {
for item, ok = next(); ok; item, ok = next() {
if item.(int) > threshold {
return
}
}
return
}
},
}
}
result := MyQuery(Range(1,10)).GreaterThan(5).Results()
Generic Functions
Although Go doesn't implement generics, with some reflection tricks, you can use go-linq without typing interface{}s and type assertions. This will introduce a performance penalty (5x-10x slower) but will yield in a cleaner and more readable code.
Methods with T suffix (such as WhereT) accept functions with generic types. So instead of
.Select(func(v interface{}) interface{} {...})
you can type:
.SelectT(func(v YourType) YourOtherType {...})
This will make your code free of interface{} and type assertions.
Example 4: "MapReduce" in a slice of string sentences to list the top 5 most used words using generic functions
var results []string
From(sentences).
// split sentences to words
SelectManyT(func(sentence string) Query {
return From(strings.Split(sentence, " "))
}).
// group the words
GroupByT(
func(word string) string { return word },
func(word string) string { return word },
).
// order by count
OrderByDescendingT(func(wordGroup Group) int {
return len(wordGroup.Group)
}).
// order by the word
ThenByT(func(wordGroup Group) string {
return wordGroup.Key.(string)
}).
Take(5). // take the top 5
// project the words using the index as rank
SelectIndexedT(func(index int, wordGroup Group) string {
return fmt.Sprintf("Rank: #%d, Word: %s, Counts: %d", index+1, wordGroup.Key, len(wordGroup.Group))
}).
ToSlice(&results)
More examples can be found in the documentation.
Release Notes
v3.2.0 (2020-12-29)
* Added FromChannelT().
* Added DefaultIfEmpty().
v3.1.0 (2019-07-09)
* Support for Go modules
* Added IndexOf()/IndexOfT().
v3.0.0 (2017-01-10)
* Breaking change: ToSlice() now overwrites existing slice starting
from index 0 and grows/reslices it as needed.
* Generic methods support (thanks @cleitonmarx!)
- Accepting parametrized functions was originally proposed in #26
- You can now avoid type assertions and interface{}s
- Functions with generic methods are named as "MethodNameT" and
signature for the existing LINQ methods are unchanged.
* Added ForEach(), ForEachIndexed() and AggregateWithSeedBy().
v2.0.0 (2016-09-02)
* IMPORTANT: This release is a BREAKING CHANGE. The old version
is archived at the 'archive/0.9' branch or the 0.9 tags.
* A COMPLETE REWRITE of go-linq with better performance and memory
efficiency. (thanks @kalaninja!)
* API has significantly changed. Most notably:
- linq.T removed in favor of interface{}
- library methods no longer return errors
- PLINQ removed for now (see channels support)
- support for channels, custom collections and comparables
v0.9-rc4
* GroupBy()
v0.9-rc3.2
* bugfix: All() iterating over values instead of indices
v0.9-rc3.1
* bugfix: modifying result slice affects subsequent query methods
v0.9-rc3
* removed FirstOrNil, LastOrNil, ElementAtOrNil methods
v0.9-rc2.5
* slice-accepting methods accept slices of any type with reflections
v0.9-rc2
* parallel linq (plinq) implemented
* Queryable separated into Query & ParallelQuery
* fixed early termination for All
v0.9-rc1
* many linq methods are implemented
* methods have error handling support
* type assertion limitations are unresolved
* travis-ci.org build integrated
* open sourced on github, master & dev branches
![[WIP] Generic functions proposal](https://avatars.githubusercontent.com/u/2603144?v=4)
![runtime error: hash of unhashable type map[string]interface {}](https://avatars.githubusercontent.com/u/17635146?v=4)
