1 files changed, 163 insertions, 0 deletions
diff --git a/skate/set/set.go b/skate/set/set.go
new file mode 100644
index 0000000..a198094
--- /dev/null
+++ b/skate/set/set.go
@@ -0,0 +1,163 @@
+package set
+
+import (
+	"sort"
+	"strings"
+)
+
+// Set implements basic string set operations.
+type Set map[string]struct{}
+
+// Add adds an element.
+func (s *Set) Add(v string) *Set {
+	(*s)[v] = struct{}{}
+	return s
+}
+
+// Len returns number of elements in set.
+func (s *Set) Len() int {
+	return len(*s)
+}
+
+// IsEmpty returns if set has zero elements.
+func (s *Set) IsEmpty() bool {
+	return s.Len() == 0
+}
+
+// Equals returns true, if sets contain the same elements.
+func (s *Set) Equals(t *Set) bool {
+	for k := range *s {
+		if !t.Contains(k) {
+			return false
+		}
+	}
+	return s.Len() == t.Len()
+}
+
+// Contains returns membership status.
+func (s *Set) Contains(v string) bool {
+	_, ok := (*s)[v]
+	return ok
+}
+
+// Intersection returns a new set containing all elements found in both sets.
+func (s *Set) Intersection(t *Set) *Set {
+	u := New()
+	for _, v := range s.Slice() {
+		if t.Contains(v) {
+			u.Add(v)
+		}
+	}
+	return u
+}
+
+// Union returns the union of two sets.
+func (s *Set) Union(t *Set) *Set {
+	u := New()
+	for _, v := range s.Slice() {
+		u.Add(v)
+	}
+	for _, v := range t.Slice() {
+		u.Add(v)
+	}
+	return u
+}
+
+// Slice returns all elements as a slice.
+func (s *Set) Slice() (result []string) {
+	for k := range *s {
+		result = append(result, k)
+	}
+	return
+}
+
+// SortedSlice returns all elements as a slice, sorted.
+func (s *Set) SortedSlice() (result []string) {
+	for k := range *s {
+		result = append(result, k)
+	}
+	sort.Strings(result)
+	return
+}
+
+// TopK returns at most k elements.
+func (s *Set) TopK(k int) *Set {
+	var top []string
+	for i, v := range s.SortedSlice() {
+		if i < k {
+			top = append(top, v)
+		}
+	}
+	return FromSlice(top)
+}
+
+func (s *Set) Product(t *Set) (result [][]string) {
+	for k := range *s {
+		for l := range *t {
+			result = append(result, []string{k, l})
+		}
+	}
+	return
+}
+
+// Jaccard returns the jaccard index of sets s and t.
+func (s *Set) Jaccard(t *Set) float64 {
+	if s.IsEmpty() && t.IsEmpty() {
+		return 1
+	}
+	if u := s.Union(t); u.IsEmpty() {
+		return 0
+	} else {
+		return float64(s.Intersection(t).Len()) / float64(u.Len())
+	}
+}
+
+func (s *Set) Join(sep string) string {
+	return strings.Join(s.Slice(), sep)
+}
+
+// Max returns the size of the largest set.
+func Max(ss ...*Set) (max int) {
+	for _, s := range ss {
+		if s.Len() > max {
+			max = s.Len()
+		}
+	}
+	return
+}
+
+// Min returns the size of the smallest set.
+func Min(ss ...*Set) (min int) {
+	min = 2 << 30
+	for _, s := range ss {
+		if s.Len() < min {
+			min = s.Len()
+		}
+	}
+	return
+}
+
+func Filter(s *Set, f func(string) bool) *Set {
+	t := New()
+	for v := range *s {
+		if f(v) {
+			t.Add(v)
+		}
+	}
+	return t
+}
+
+// New creates a new set.
+func New() *Set {
+	s := make(Set)
+	return &s
+}
+
+// FromSlice initializes a set from a slice.
+func FromSlice(vs []string) *Set {
+	s := New()
+	for _, v := range vs {
+		s.Add(v)
+	}
+	return s
+}