How Can I Efficiently Sort a Go Array of Structs by a Custom Field Name?

Efficient Array Sorting by Custom Field Names

Sorting data structures is a fundamental task in programming, and Go offers various approaches to handle this. In particular, arrays of structs pose a challenge when sorting based on arbitrary field names.

Problem Statement

Consider the following Go code:

type Planet struct {
    Name       string  `json:"name"`
    Aphelion   float64 `json:"aphelion"`   // in million km
    Perihelion float64 `json:"perihelion"` // in million km
    Axis       int64   `json:"Axis"`       // in km
    Radius     float64 `json:"radius"`
}

func main() {
    planets := [...]Planet{{"Mars", 249.2, 206.7, 227939100, 3389.5},
                         {"Venus", 108.939, 107.477, 108208000, 6051.8},
                         {"Earth", 151.930, 147.095, 149598261, 6371.0}}
}

How can we sort the planets array by the Axis field?

Solution

In recent versions of Go, the sort.Slice function provides an efficient way to sort slices based on a custom comparison function.

sort.Slice(planets[:], func(i, j int) bool {
  return planets[i].Axis < planets[j].Axis
})

Here, i and j are indices of elements in the slice, and the comparison function returns true if the element at index i should come before the element at index j. In this case, we're comparing the Axis fields of the planets.

Note that when using arrays (as opposed to slices), the slice overlay operator [:] is required to convert the array to a slice.

Conclusion

By leveraging sort.Slice, we achieve simple and efficient sorting of arrays of structs based on arbitrary field names. This provides a Python-like experience for sorting complex data structures in Go.

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