The missing slice package

A Go-generics (Go 1.18) based functional library with no side-effects that adds the following functions to a slice package:

  • Unique(): removes duplicate items from a slice
  • SortedUnique(): removes duplicate items from a sorted slice. Fast!
  • Sort(): Sorts a slice
  • SortBy(): Sorts a slice by arbitrary criteria
  • Compare(): Iterates two slices comparing them together
  • Subtract(): subtract one slice from another
  • Map(): map over a slice and transform it
  • Reduce(): reduce a slice to a single value
  • Index(): return the index of an element
  • SortedIndex(): return the index of an element in a sorted list. Fast!
  • First(): return the first element
  • Last(): return the last element
  • Select(): select all elements matching some specified criteria
  • Contains(): returns true if the slice contains an element
  • SortedContains(): returns true if the sorted slice contains an element. Fast!
  • Pop(): pop the last element off the list
  • Shift(): shift the first element off the list
  • Unshift(): shift an element into the first place (prepend)
  • Find(): find the first element in a slice that matches some criteria

Method signatures:

(where T is almost any type)

  • slice.Unique([]T) []T
  • slice.SortedUnique([]T) []T
  • slice.Sort([]T) []T
  • slice.SortBy([]T, sortFunc func(slice []T, i, j int) bool) []T
  • slice.Compare(s1, s2 []T, left, equal, right func(elem T))
  • slice.Subtract(s1, s2 []T) []T
  • slice.Map([]T, func(i int, elem T) T) []T
  • slice.Reduce(items []T, initialAccumulator T, f AccumulatorFunc[T]) T
  • slice.Index([]T, elem T) int
  • slice.SortedIndex([]T, elem T) int
  • slice.First([]T) (T, bool)
  • slice.Last([]T) (T, bool)
  • slice.Select([]T, func(i int, elem T) T) []T
  • slice.Contains([]T, elem T) bool
  • slice.SortedContains([]T, elem T) bool
  • slice.Pop([]T) (T, []T)
  • slice.Shift([]T) (T, []T)
  • slice.Unshift([]T, elem T) []T
  • slice.Find([]T, func(i int, elem T) T) (elem T, found bool)

Note the AccumulatorFunc signature is func(acc T, i int, elem T) T


See tests for more examples. Here are a few:

  // sum function implemented with Reduce
  input := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
	result := slice.Reduce(input, 0, func(acc int, i int, elem int) string {
		return acc + elem
  // result == 55


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