Clojure Transducers — Pipelines Without Intermediate Collections | Episode 18

A threaded pipeline reads great but builds a new lazy sequence at every step. For small data that's fine. For large data, all those intermediate collections add up. Transducers let you describe the same pipeline once, and apply it to a collection in a single pass — no intermediate collections, no wasted allocations. In this episode we cover what a transducer is, how to compose transducers with comp, applying them with transduce and into, and rewriting Episode 14's pipeline as a transducer. Student code: https://github.com/GoCelesteAI/clojure-for-beginners/tree/main/episode18 Every keystroke is shown on screen with generous pauses so you can follow along at your own pace. What You'll Learn: - What a transducer is — a reducing function transformer - Creating one by calling map, filter, etc. without a collection - Composing with comp (left-to-right, the reverse of regular comp intuition) - transduce — apply and fold in one pass - into — collect into a new collection directly - Rewriting Episode 14's pipeline as a transducer Timestamps: 0:00 - Intro 0:15 - Preview: pipelines without intermediate collections 0:38 - Start the REPL 0:52 - map without a coll = transducer 1:13 - Compose with comp 1:30 - transduce and into in the REPL 1:49 - Exit REPL 2:03 - Write transducers.clj in Neovim 2:31 - Transducer section 3:34 - Compose section 4:34 - transduce section 5:32 - into section 6:17 - Ep14 pipeline, as a transducer 8:21 - Run with clj -M 8:25 - Output walked through 9:29 - Review 9:38 - Recap 10:16 - What's next: Episode 19 Key Takeaways: 1. A transducer is a transformation, independent of the collection type. 2. comp composes transducers left-to-right — (comp f1 f2) applies f1 then f2. 3. transduce applies a transducer and folds with a reducing function. 4. into applies a transducer and collects into a target collection type. 5. Same pipeline, one pass, zero intermediate collections. Phase 3 continues. Next up, Episode 19 — for, doseq, and list comprehensions. Taught by CelesteAI. Like and subscribe for more Clojure tutorials!