github.com/monmaru/go-linq

go-linq

A powerful language integrated query (LINQ) library for Go.

• Written in vanilla Go!
• Safe for concurrent use
• Complete lazy evaluation with iterator pattern
• Supports arrays, slices, maps, strings, channels and custom collections (collection needs to implement Iterable interface and element - Comparable interface)

Installation

$ go get github.com/ahmetalpbalkan/go-linq

:warning: :warning: go-linq has recently introduced breaking API changes with v2.0.0. See release notes for details. v2.0.0 comes with a refined interface, dramatically increased performance and memory efficiency, and new features such as lazy evaluation (read more).

The old version is still available in archive/0.9 branch and tagged as 0.9 as well. If you are using go-linq, please vendor a copy of it in your source tree to avoid getting broken by upstream changes.

Quickstart

Usage is as easy as chaining methods like:

From(slice) .Where(predicate) .Select(selector) .Union(data)

Example: Find all owners of cars manufactured from 2015

import . "github.com/ahmetalpbalkan/go-linq"
	
type Car struct {
    id, year int
    owner, model string
}

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)

Example: Find the author who has written the most books

import . "github.com/ahmetalpbalkan/go-linq"
	
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: 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()

More examples can be found in documentation.

Release Notes

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