sorting.md

Overview

• Idioms for sorting collections

Slices

1. For builtin types:

    // -- sort ints
    myInts := []int{3, 5, 2}
    sort.Ints(myInts)

    fmt.Printf("%v", myInts) // [2 3 5]

    // -- sort floats
    myFloats := []float64{3.3, 5.5, 2.1}
    sort.Float64s(myFloats)

    fmt.Printf("%v", myFloats) // [2.1 3.3 5.5]

    // -- sort strings
    s := []string{"c", "a", "b"}
    sort.Strings(s)

    fmt.Printf("%v", s) // [a b c]

1. For custom types

type Car struct {
    Model string
    Year  int32
}

func main() {
    cars := []Car{
        Car{Model: "X3", Year: 2020},
        Car{Model: "GLE", Year: 2022},
        Car{Model: "Jetta", Year: 2011},
    }

    // -- Sort cars by Year,
    // Stable means "when year is same, retain original order"
       sort.SliceStable(
        cars,
        func(i, j int) bool {
            return cars[i].Year < cars[j].Year
        })
}

Sort by multiple fields

type Foo struct {
    A, B, C string
}

...
    sort.Slice(foos, func(i, j int) bool {
        switch {
        case foos[i].A != foos[j].A:
            return foos[i].A < foos[j].A

        case foos[i].B != foos[j].B:
            return foos[i].B < foos[j].B

        default:
            return foos[i].C < foos[j].C
        }
    })

Maps

1. Example

TODO: copy keys into slice, sort the slice, lookup via keys

1. Note that fmt.Print* prints maps with keys sorted

Sets

1. Example

TODO: copy into slice, sort the slice

Other Resources

1. https://gobyexample.com/sorting
2. https://gobyexample.com/sorting-by-functions
3. reversing
4. sort.Slice
5. sort.SliceStable
6. https://www.practical-go-lessons.com/chap-16-interfaces#sort.interface
7. https://yourbasic.org/golang/how-to-sort-in-go/
8. Sorting, in general