What is the shortest way to simply sort an array of structs by (arbitrary) field names?

Question

I just had a problem where I had an array of structs, e.g.

package main

import "log"

type Planet struct {
    Name       string  `json:"name"`
    Aphelion   float64 `json:"aphelion"`   // in million km
    Perihelion float64 `json:"perihelion"` // in million km
    Axis       int64   `json:"Axis"`       // in km
    Radius     float64 `json:"radius"`
}

func main() {
    var mars = new(Planet)
    mars.Name = "Mars"
    mars.Aphelion = 249.2
    mars.Perihelion = 206.7
    mars.Axis = 227939100
    mars.Radius = 3389.5

    var earth = new(Planet)
    earth.Name = "Earth"
    earth.Aphelion = 151.930
    earth.Perihelion = 147.095
    earth.Axis = 149598261
    earth.Radius = 6371.0

    var venus = new(Planet)
    venus.Name = "Venus"
    venus.Aphelion = 108.939
    venus.Perihelion = 107.477
    venus.Axis = 108208000
    venus.Radius = 6051.8

    planets := [...]Planet{*mars, *venus, *earth}
    log.Println(planets)
}

Lets say you want to sort it by Axis. How do you do that?

(Note: I have seen http://golang.org/pkg/sort/ and it seems to work, but I have to add about 20 lines just for simple sorting by a very simple key. I have a python background where it is as simple as sorted(planets, key=lambda n: n.Axis) - is there something similar simple in Go?)

Answer 1

As of Go 1.8 you can now use sort.Slice to sort a slice:

sort.Slice(planets, func(i, j int) bool {
  return planets[i].Axis < planets[j].Axis
})

---

There is normally no reason to use an array instead of a slice, but in your example you are using an array, so you have to overlay it with a slice (add [:]) to make it work with sort.Slice:

sort.Slice(planets[:], func(i, j int) bool {
  return planets[i].Axis < planets[j].Axis
})

The sorting changes the array, so if you really want you can continue to use the array instead of the slice after the sorting.