xforms/README.md

xforms

More transducers and reducing functions for Clojure!

Transducers: reduce, into, by-key, partition, pad and for.

Reducing functions: str, str!, avg, count, juxt, juxt-map.

Usage

Add this dependency to your project:

[net.cgrand/xforms "0.1.0-SNAPSHOT"]

=> (require '[net.cgrand.xforms :as x])

str and str! are two reducing functions to build Strings and StringBuilders in linear time.

=> (quick-bench (reduce str (range 256)))
             Execution time mean : 58,714946 µs
=> (quick-bench (reduce x/str (range 256)))
             Execution time mean : 11,609631 µs

for is the transducing cousin of clojure.core/for:

=> (quick-bench (reduce + (for [i (range 128) j (range i)] (* i j))))
             Execution time mean : 514,932029 µs
=> (quick-bench (transduce (x/for [i % j (range i)] (* i j)) + 0 (range 128)))
             Execution time mean : 373,814060 µs

by-key and reduce are two new transducers. Here is an example usage:

;; reimplementing group-by
(defn my-group-by [kfn coll]
  (into {} (x/by-key kfn (x/reduce conj)) coll))

;; let's go transient!
(defn my-group-by [kfn coll]
  (into {} (x/by-key kfn (x/into [])) coll))

=> (quick-bench (group-by odd? (range 256)))
             Execution time mean : 29,356531 µs
=> (quick-bench (my-group-by odd? (range 256)))
             Execution time mean : 20,604297 µs

Like by-key, partition also takes a transducer as an argument to allow further computation on the partition without buffering.

=> (sequence (x/partition 4 (x/reduce +)) (range 16))
(6 22 38 54)

Padding can be achieved using the pad function:

=> (sequence (x/partition 4 (comp (x/pad 4 (repeat :pad)) (x/into []))) (range 9))
([0 1 2 3] [4 5 6 7] [8 :pad :pad :pad])

avg is a reducing fn to compute the arithmetic mean. juxt and juxt-map are used to compute several reducing fns at once.

=> (into {} (x/by-key odd? (x/reduce (x/juxt + x/avg))) (range 256))
{false [16256 127], true [16384 128]}
=> (into {} (x/by-key odd? (x/reduce (x/juxt-map :sum + :mean x/avg :count x/count))) (range 256))
{false {:sum 16256, :mean 127, :count 128}, true {:sum 16384, :mean 128, :count 128}}

License

Copyright © 2015 Christophe Grand

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.