• Clojure

(def items [1 2 3 4 4 5 5 5])

(def c (count (set items)))

• C#

int c = items.Distinct().Count();

• Dart

var c = items.toSet().length;

• Elixir

c = items |> Enum.uniq |> length

• Go

func count[T comparable](items []T) int {
	distinct := make(map[T]bool)
	for _, v := range items {
		distinct[v] = true
	}
	return len(distinct)
}

• Go

distinct := make(map[T]bool)
for _, v := range items {
	distinct[v] = true
}
c := len(distinct)

• Haskell

c = count . nub $ items

• JS

const c = new Set(items).size;

• Java

long c = items.stream().distinct().count();

• Kotlin

val c = items.distinct().size

• Lua

local undupeitems = {}
for _, v in ipairs(items) do
local undupe = true
if #undupeitems == 0 then
  table.insert(undupeitems, v)
else
  for _, v2 in ipairs(undupeitems) do
    if v == v2 then
      undupe = false
    end
  end
  if undupe then
  table.insert(undupeitems, v)
  end
end

end
local c=#undupeitems

• PHP

$c = count(array_unique($items));

• Pascal

function CountUniqueItems(Items: TStrings): Integer;
var
  List: TStringList;
begin
  List := TStringList.Create;
  List.Duplicates := dupIgnore;
  List.Sorted := True;
  List.AddStrings(Items);
  Result := List.Count;
  List.Free;
end;

begin
 ...
 c := CountUniqueItems(items);
 ...
end.

• Perl

my $c = scalar(uniq @items);

• Python

c = len({*items})

• Python

array = []
for value in items:
    if value not in array:
        array.append(value)
c = len(array)

• Python

c = 0
for index, value in enumerate(items):
    if value not in items[index + 1:]:
        c += 1

• Python

c = len(set(items))

• Ruby

c = items.uniq.count

• Rust

let c = items.iter().unique().count();