Sort on map on value (attribute of Struct) - sorting

Question

I have the below map:
detail := make(map[string]*Log)
type Log struct {
Id []string
Name []string
Priority int // value could be 1, 2, 3
Message string
}
I want to sort the "detail" map on basis of the value which is a struct in my case. This should be sorted by attribute "Priority".
For example, Log (map of struct) may have values similar to below:
Z : &{[ba60] [XYZ] 3 "I am the boss"}
B : &{[ca50] [ABC] 2 "I am the Junior"}
U : &{[zc20] [PQR] 1 "I am the Newbie"}
I want them to print from increasing Priority order i.e. 1 to 3
U : &{[zc20] [PQR] 1 "I am the Newbie"}
B : &{[ca50] [ABC] 2 "I am the Junior"}
Z : &{[ba60] [XYZ] 3 "I am the boss"}
I tried to use the sort and implemented the Sort interface, but seems like still missing the clue somewhere. So, I implemented the below interface:
type byPriority []*Log
func (d byPriority) Len() int {
return len(d)
}
func (d byPriority) Less(i, j int) bool {
return d[i].Priority < d[j].Priority
}
func (d byPriority) Swap(i, j int) {
d[i], d[j] = d[j], d[i]
}
But how should I apply sort.Sort() method on this map to get the sorted result. Do I need to add some more code?

Answer 1

The map type in Go is unordered. Regardless of what you do to a map, the next time you iterate over it you will receive the keys in random order. Thus there is no way to "sort" a map.
What you can do is copy the entries of the map into a slice, which is sortable.
package main
import (
"fmt"
"sort"
)
type Log struct {
Id []string
Name []string
Priority int // value could be 1, 2, 3
Message string
}
type Entry struct {
key string
value *Log
}
type byPriority []Entry
func (d byPriority) Len() int {
return len(d)
}
func (d byPriority) Less(i, j int) bool {
return d[i].value.Priority < d[j].value.Priority
}
func (d byPriority) Swap(i, j int) {
d[i], d[j] = d[j], d[i]
}
func printSorted(detail map[string]*Log) {
// Copy entries into a slice.
slice := make(byPriority, 0, len(detail))
for key, value := range detail {
slice = append(slice, Entry{key, value})
}
// Sort the slice.
sort.Sort(slice)
// Iterate and print the entries in sorted order.
for _, entry := range slice {
fmt.Printf("%s : %v\n", entry.key, entry.value)
}
}
func main() {
detail := map[string]*Log{
"Z": &Log{[]string{"ba60"}, []string{"XYZ"}, 3, "I am the boss"},
"B": &Log{[]string{"ca50"}, []string{"ABC"}, 2, "I am the Junior"},
"U": &Log{[]string{"zc20"}, []string{"PQR"}, 1, "I am the Newbie"},
}
printSorted(detail)
}