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Chaining map and filter creates intermediate sequences. Transducers describe the transformation once and apply it without those intermediates.

Calling map or filter with a single argument returns a transducer, a transformation recipe with no collection attached.

Combine transducers with comp. Note they apply left to right, unlike ordinary function composition.

Use into with a transducer to build a concrete collection efficiently.

transduce reduces with a transducer in one pass, like a turbocharged reduce.

Because the transducer threads each element through the whole pipeline before moving on, it never materializes the in-between sequences. This saves memory on large data.

The same transducer works on a vector, a channel, or a lazy seq. The recipe is decoupled from where the data comes from.

Stateful transducers like take can stop the pipeline early, which pairs well with infinite or expensive sources.

Lazy seqs defer work; transducers eliminate intermediate allocation. For tight numeric pipelines, transducers are typically faster and create less garbage.

Define a transducer once and reuse it across many call sites and many collection types. This is the core win: a transformation that is a value.

Use transducers for hot paths, large data, or when feeding core.async channels. For small, simple chains, plain map/filter stay clearer.

Test your transducer knowledge.

You learned transducers as composable, source-independent recipes, building them with comp, applying with into/transduce/sequence, early termination, and when they beat lazy seqs.