`distinct` removes repeated values from a collection, retaining each value’s first occurrence. It returns a lazy sequence, so the result follows the input’s order rather than sorting it. Duplicate detection uses Clojure’s equality semantics for both scalar values and collections. section 10.8 section 6.1
Keep the first occurrence
```clojure (distinct [1 2 1 1 3 2 4 1]) ;; (1 2 3 4) ``` Later appearances of `1` and `2` disappear, even when they are separated from their first appearances. section 10.8
Choose the operation that matches the job:
- `(dedupe [1 2 1 1 3 2 4 1])` returns `(1 2 1 3 2 4 1)`: it removes only contiguous repetitions. section 10.8
- `distinct?` reports whether its arguments are all different; it returns a boolean rather than a sequence and requires at least one argument. section 10.8
- `set` also removes duplicates, but its result does not retain the sequence’s order. section 10.8
With no argument, `(distinct)` returns a transducer. It can follow other transformations in `comp`; for example, `(sequence (comp (map range) cat (distinct)) (range 10))` yields `(0 1 2 3 4 5 6 7 8)`. The collection argument may be `nil`, but `distinct` does not accept sets, maps, or transients. Use it when repeated values must be removed across the whole input, not merely when adjacent values match. section 10.8 section 7.2
