Sort a custom struct array in GoLang

Question

How do I sort a custom array of struct using GoLang.

My Code is :

package main

import "fmt"

type TicketDistribution struct {
    Label        string
    TicketVolume int64
}

type TicketDistributionResponse struct {
    LevelDistribution []*TicketDistribution
}

func main() {
    var response TicketDistributionResponse

    response.LevelDistribution = append(response.LevelDistribution, &TicketDistribution{Label: "John", TicketVolume: 3})
    response.LevelDistribution = append(response.LevelDistribution, &TicketDistribution{Label: "Bill", TicketVolume: 7})
    response.LevelDistribution = append(response.LevelDistribution, &TicketDistribution{Label: "Sam", TicketVolume: 4})

    for _, val := range response.LevelDistribution {
        fmt.Println(*val)
    }

}

This prints the output as

{John 3}
{Bill 7}
{Sam 4}

I want to sort the response object by TicketVolume value in descending order.

After the sort the response object should look like :

{Bill 7}
{Sam 4}
{John 3}

Answer 1

You can use sort.Slice for that. It takes your slice and a sort function. The sort function itself takes two indices and returns true if the left item is smaller than the right one.

This way you can sort by your own custom criteria.

package main

import (
    "fmt"
    "sort"
)

type TicketDistribution struct {
    Label        string
    TicketVolume int64
}

type TicketDistributionResponse struct {
    LevelDistribution []*TicketDistribution
}

func main() {
    var response TicketDistributionResponse

    response.LevelDistribution = append(response.LevelDistribution, &TicketDistribution{Label: "John", TicketVolume: 3})
    response.LevelDistribution = append(response.LevelDistribution, &TicketDistribution{Label: "Bill", TicketVolume: 7})
    response.LevelDistribution = append(response.LevelDistribution, &TicketDistribution{Label: "Sam", TicketVolume: 4})

    sort.Slice(response.LevelDistribution, func(i, j int) bool {
        a := response.LevelDistribution[i]
        b := response.LevelDistribution[j]
        return a.TicketVolume > b.TicketVolume
    })

    for _, val := range response.LevelDistribution {
        fmt.Println(*val)
    }
}

The use of > in the comparison function sorts the slice descendingly, for ascending order you would use <.