Thanks for the reply. I do like this. I think it's actually more elegant.
Definitely going into my toolbox. One thing I dislike is that I still have
to re-implement the logic of the already existing (performant tested)
transducers.
Also, I could also add a 4th parameter: 'terminate-early?' but that's then
already 4 parameters to remember... I'll have to see what way is best once
I implement more transducers with your or my (hacky) method.
Cheers
On Monday, May 11, 2015 at 1:34:31 PM UTC-4, miner wrote:
Not an expert, but I’ll throw out an alternative approach that might work
for you. I think it’s simpler to use a transducer that calls functions
rather than trying to transform an existing transducer to do the cutoff.
(defn take-while-accumulating [accf init pred2]
(fn [rf]
(let [vstate (volatile! init)]
(fn
([] (rf))
([result] (rf result))
([result input]
(if (pred2 @vstate input)
(do (vswap! vstate accf input)
(rf result input))
(reduced result)))
accf is like a reducing function: takes two args, state and input, and
returns new state of the “accumulation”. init is the initial state of the
accumulation. pred2 is a predicate taking two args, the accumulation state
and the new input. The process stops when pred2 returns false.
;; distinct
(into [] (take-while-accumulating conj #{} (complement contains?)) '(1 2 3
4 2 5 6))
;;= [1 2 3 4]
;; dedupe
(into [] (take-while-accumulating (fn [r x] x) ::void not=) '(1 2 1 3 4 4
5 6))
;;= [1 2 1 3 4]
;; monotonically increasing
(into [] (take-while-accumulating max 0 =) '(1 2 3 4 4 1 5 6))
[1 2 3 4 4]
Steve Miner
steve...@gmail.com javascript:
On May 9, 2015, at 6:28 PM, Andy- andre...@gmail.com javascript:
wrote:
(defn take-while-xf
Takes a transducer and returns a transducer that will immediately
finish (ie
call (reduced)) when the transducer did not call the reducing function
and
just returned the result. Only really useful with stateful
transducers.
Otherwise you'd use take-while.
[xf]
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