How to Sort Structs in Go by Multiple Criteria (LastName then FirstName)?

Sorting Structs with Multiple Criteria

In Go, sorting a slice of structs can be achieved using various approaches. This discussion focuses on sorting by multiple parameters, specifically by LastName and then FirstName.

Method 1: slices.SortFunc (Go 1.22 )

For Go 1.22 and above, slices.SortFunc provides an elegant solution:

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

Method 2: sort.Slice or sort.Sort

In Go 1.8 , sort.Slice or sort.Sort can be used. Both require a less function to determine the ordering. This function compares the LastName and FirstName fields:

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
})

For sort.Sort, a custom type implementing the sort.Interface is needed:

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

Choose the approach that best suits your application's requirements. Unless performance analysis reveals sorting to be a bottleneck, convenience should be prioritized.

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