Sets of cards in the Golang

Question

If I have a structure like:

type Foo struct {
  title string
  Tags map[string]string
}

How can one approach the preservation of a unique set of such structures? From what I understand, although structural equality is a thing - map equality is not. This means that I can not compare my above structure. Therefore, I can’t just implement the map as a given template .

Two options that may work, I can think of: convert tags to sorted [][]stringor use reflect.Deepequal . Anyone have a better idea?

Answer 1

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package structset

type Foo struct {
  title string
  Tags  map[string]string
}

func (f Foo) Equals(f2 Foo) bool {
  if f.title != f2.title {
    return false
  }

  if len(f.Tags) != len(f2.Tags) {
    return false
  }

  for k, v := range f.Tags {
    if w, ok := f2.Tags[k]; !ok || v != w {
      return false
    }
  }

  return true
}

type FooSet []Foo

func (this FooSet) Add(value Foo) {
  if !this.Contains(value) {
    this = append(this, value)
  }
}

func (this FooSet) Length() int {
  return len(this)
}

func (this FooSet) Contains(f Foo) bool {
  for _, v := range this {
    if v.Equals(f) {
      return true
    }
  }
  return false
}

func NewSet() FooSet {
  return FooSet(make([]Foo, 0, 100))
}

i7-3770K Windows :

BenchmarkSmallSetWithFewCollisions         50000             46615 ns/op
BenchmarkSmallSetWithMoreCollisions        50000             46575 ns/op
BenchmarkSmallSetWithManyCollisions        50000             46605 ns/op
BenchmarkMediumSetWithFewCollisions         1000           2335296 ns/op
BenchmarkMediumSetWithMoreCollisions        1000           2352298 ns/op
BenchmarkMediumSetWithManyCollisions        1000           2336796 ns/op
BenchmarkLargeSetWithFewCollisions            50          46805944 ns/op
BenchmarkLargeSetWithMoreCollisions           50          47376016 ns/op
BenchmarkLargeSetWithManyCollisions           50          46815946 ns/op

, , .

:

func (this FooSet) RemoveDuplicates() {
  length := len(this) - 1
  for i := 0; i < length; i++ {
    for j := i + 1; j <= length; j++ {
      if this[i].Equals(this[j]) {
        this[j] = this[length]
        this = this[0:length]
        length--
        j--
      }
    }
  }
}

:

BenchmarkSmallSetWithFewCollisions         50000             45245 ns/op
BenchmarkSmallSetWithMoreCollisions        50000             45615 ns/op
BenchmarkSmallSetWithManyCollisions        50000             45555 ns/op
BenchmarkMediumSetWithFewCollisions         1000           2294791 ns/op
BenchmarkMediumSetWithMoreCollisions        1000           2309293 ns/op
BenchmarkMediumSetWithManyCollisions        1000           2286290 ns/op
BenchmarkLargeSetWithFewCollisions            50          46235870 ns/op
BenchmarkLargeSetWithMoreCollisions           50          46515906 ns/op
BenchmarkLargeSetWithManyCollisions           50          45865824 ns/op

Foo [string] Foo.

BenchmarkSmallSetWithFewCollisions         50000             65718 ns/op
BenchmarkSmallSetWithMoreCollisions        50000             64238 ns/op
BenchmarkSmallSetWithManyCollisions        50000             55016 ns/op
BenchmarkMediumSetWithFewCollisions          500           3429435 ns/op
BenchmarkMediumSetWithMoreCollisions         500           3117395 ns/op
BenchmarkMediumSetWithManyCollisions        1000           2826858 ns/op
BenchmarkLargeSetWithFewCollisions            20          82635495 ns/op
BenchmarkLargeSetWithMoreCollisions           20          85285830 ns/op
BenchmarkLargeSetWithManyCollisions           20          73659350 ns/op

, , .

Answer 2

, , , . , .

- :

// Doesn't have to be a string: just has to be suitable for use as a map key.
func (foo *Foo) key() string {
    return key_string
}

fooSet := make(map[string] *Foo)

// Store a Foo
fooSet[x.key()] = x

// Check if x is in the set:
if fooSet[x.key()] != nil {
    println("x is in the set")
}

, , .

Answer 3

Are you sure your example works? I believe that you need to pass a pointer to the Add () method for your code to work. Anyway, here is my implementation:

package math

// types

type IntPoint struct {
    X, Y int
}

// set implementation for small number of items
type IntPointSet struct {
    slice []IntPoint 
}

// functions

func (p1 IntPoint) Equals(p2 IntPoint) bool {
    return (p1.X == p2.X) && (p1.Y == p2.Y)
}

func (set *IntPointSet) Add(p IntPoint) {
    if ! set.Contains(p) {
        set.slice = append(set.slice, p)
    }
}

func (set IntPointSet) Contains(p IntPoint) bool {
  for _, v := range set.slice {
    if v.Equals(p) {
      return true
    }
  }
  return false
}

func (set IntPointSet) NumElements() int {
    return len(set.slice)
}

func NewIntPointSet() IntPointSet {
  return IntPointSet{(make([]IntPoint, 0, 10))}
}