Sort array of maps using keys matching a value GO

Question

I have just started programming in Golang and want to sort an array of maps. I have an array of maps. Let's call it example_array.

example_array = [
  [
    { Name: "A", Value: 100 }, 
    { Name: "B", Value: 60 }, 
    { Name: "C", Value: 170 }, 
    { Name: "D", Value: 120} 
  ], 
  [
    { Name: "A", Value: 64 }, 
    { Name: "B", Value: 90 }, 
    { Name: "C", Value: 52 }, 
    { Name: "D", Value: 98} 
  ], 
  [
    { Name: "A", Value: 154 }, 
    { Name: "B", Value: 190 }, 
    { Name: "C", Value: 179 }, 
    { Name: "D", Value: 67 } 
  ]

]

Now I want to sort this array using value of key "C" so the example_array should be modified to ->

[
[{Name: "A", Value: 64}, {Name: "B", Value: 90}, {Name: "C", Value: 52}, {Name: "D", Value: 98}],
[{Name: "A", Value: 100}, {Name: "B", Value: 60}, {Name: "C", Value: 170}, {Name: "D", Value: 120}], 
[{Name: "A", Value: 154}, {Name: "B", Value: 190}, {Name: "C", Value: 179}, {Name: "D", Value: 67}]
]

If I sort the original array using value of key "D", the original array should be modified to ->

[
[{Name: "A", Value: 154}, {Name: "B", Value: 190}, {Name: "C", Value: 179}, {Name: "D", Value: 67}],
[{Name: "A", Value: 64}, {Name: "B", Value: 90}, {Name: "C", Value: 52}, {Name: "D", Value: 98}]
[{Name: "A", Value: 100}, {Name: "B", Value: 60}, {Name: "C", Value: 170}, {Name: "D", Value: 120}]
]

How can I sort these array of maps in Golang. Please help!

Answer 1

Your data looks like it could be easily represented as a slice of maps of type map[string]int. Since you didn't provide any Go code in your question, I cannot be sure of the data types, so I will assume it is a slice of maps of type map[string]int in this answer.

A simple way to sort a slice of maps is to use the sort.Slice function. From a comment in the first example in the sort package documentation:

use sort.Slice with a custom Less function, which can be provided as a closure. In this case no methods are needed

The Less function needs to satisfy the signature

func(i, j int) bool

Per package documentation (at Interface):

Less reports whether the element with index i should sort before the element with index j.

Using a closure allows you to reference your data structure in the function body even though it is not part of the parameter list.

Here's a runnable example that sorts a slice of map[string]int values matching the data in your question:

package main

import(
    "fmt"
    "sort"
)

func main() {
    in := []map[string]int{
        {
          "A": 100,
          "B": 60,
          "C": 170,
          "D": 120,
        },
        {
          "A": 64,
          "B": 90,
          "C": 52,
          "D": 98,
        },
        {
          "A": 154,
          "B": 190,
          "C": 179,
          "D": 67,
        },
    }
    for k, _ := range in[0] {
        sort.Slice(in, func(i, j int) bool { return in[i][k] < in[j][k] })
        fmt.Printf("By %s: %v\n", k, in)
    }
}

Output:

By A: [map[A:64 B:90 C:52 D:98] map[A:100 B:60 C:170 D:120] map[A:154 B:190 C:179 D:67]]
By B: [map[A:100 B:60 C:170 D:120] map[B:90 C:52 D:98 A:64] map[C:179 D:67 A:154 B:190]]
By C: [map[A:64 B:90 C:52 D:98] map[A:100 B:60 C:170 D:120] map[A:154 B:190 C:179 D:67]]
By D: [map[A:154 B:190 C:179 D:67] map[B:90 C:52 D:98 A:64] map[A:100 B:60 C:170 D:120]]