feat(Go-Tool)：2020/11/23：修改项目案例(按照一定规则对一组数据进行排序分组)
This commit is contained in:
Huangzj
+222
@@ -0,0 +1,222 @@
|
||||
# go-linq [](https://godoc.org/github.com/ahmetalpbalkan/go-linq) [](https://travis-ci.org/ahmetalpbalkan/go-linq) [](https://coveralls.io/github/ahmetalpbalkan/go-linq?branch=master) [](https://goreportcard.com/report/github.com/ahmetalpbalkan/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
|
||||
|
||||
$ go get github.com/ahmetalpbalkan/go-linq
|
||||
|
||||
We recommend using a dependency manager (e.g. [govendor][govendor] or
|
||||
[godep][godep]) to maintain a local copy of this package in your project.
|
||||
|
||||
[govendor]: https://github.com/kardianos/govendor
|
||||
[godep]: https://github.com/tools/godep/
|
||||
|
||||
> :warning: :warning: `go-linq` has recently introduced _breaking API changes_
|
||||
> with v2.0.0. See [release notes](#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](http://kalan.rocks/2016/07/16/manipulating-data-with-iterators-in-go/)).
|
||||
>
|
||||
> 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 1: Find all owners of cars manufactured after 2015**
|
||||
|
||||
```go
|
||||
import . "github.com/ahmetalpbalkan/go-linq"
|
||||
|
||||
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):
|
||||
|
||||
```go
|
||||
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**
|
||||
|
||||
```go
|
||||
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 3: Implement a custom method that leaves only values greater than the specified threshold**
|
||||
|
||||
```go
|
||||
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**
|
||||
|
||||
```go
|
||||
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](https://godoc.org/github.com/ahmetalpbalkan/go-linq).
|
||||
|
||||
## Release Notes
|
||||
|
||||
~~~
|
||||
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
|
||||
~~~
|
||||
Reference in New Issue
Block a user