How to Sort Structs by Multiple Parameters in Go?

Sorting Structs with Multiple Parameters

Question:

How can an array of structs be sorted by multiple parameters, specifically by last name and then first name in Go?

Answer:

There are several approaches to sorting structs with multiple parameters in Go.

Go 1.22 with slices.SortFunc

The latest version of Go (1.22 and later) offers a concise solution using slices.SortFunc:

slices.SortFunc(members, func(a, b Member) int {
    return cmp.Or(
        cmp.Compare(a.LastName, b.LastName),
        cmp.Compare(a.FirstName, b.FirstName),
    )
})

sort.Slice or sort.Sort Functions

For earlier versions of Go, consider using sort.Slice or sort.Sort. Both require a custom less function that determines the ordering based on the desired parameters.

With sort.Slice:

sort.Slice(members, func(i, j int) bool {
    if members[i].LastName != members[j].LastName {
        return members[i].LastName < members[j].LastName
    }
    return members[i].FirstName < members[j].FirstName
})

With sort.Sort:

Create a custom type that implements the sort.Interface interface, defining the Len, Swap, and Less methods.

type byLastFirst []Member

func (members byLastFirst) Len() int           { return len(members) }
func (members byLastFirst) Swap(i, j int)      { members[i], members[j] = members[j], members[i] }
func (members byLastFirst) Less(i, j int) bool {
    if members[i].LastName != members[j].LastName {
        return members[i].LastName < members[j].LastName
    }
    return members[i].FirstName < members[j].FirstName
}

sort.Sort(byLastFirst(members))

Performance Considerations:

While these approaches provide different ways to sort structs, performance analysis is crucial to optimize for hot spots. Choose the approach that best suits your application's requirements.

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