Here are two different ways of rewriting that mapc with iter: `(iter top (repeat 1) (iter (for x in '(1 2 3)) (in top (collect x))))` `(iter (repeat 1) (appending '(1 2 3)))` `(iter (repeat 1) (appending (iter (for x in '(1 2 3)) (collect x))))` If I am using iter, I try hard to *only* use iter, as one of the reasons for this library (for me) is to have a single syntax for iteration. That said, I wrote the `collectors` library to handle arbitrary collection tasks that were not easily expressed as a straight iteration. The collectors library binds local functions, so you can `(mapc #'collect ...)` etc. https://github.com/AccelerationNet/collectors Cheers, Russ Tyndall On 03/13/2018 11:52 AM, Luís Oliveira wrote:
Just a curiosity: you could compute the average incrementally: <https://math.stackexchange.com/questions/106700/incremental-averageing>, but doing it the usual way is probably more efficient and with smaller numeric error when using floats.
Slightly off-topic question: oftentimes I have to use map-like iterators. Is there a good way to use such iterators in conjunction with iter? An obvious way would be something like:
(iter (repeat 1) (mapc (lambda (x) (collect x)) '(1 2 3)))
The (iter (repeat 1) ...) bit could be hidden under a macro, I suppose. But it'd be nicer if collect were a function, so I could do (mapc #'collect '(1 2 3)). Perhaps said macro could rewrite #'clause to (lambda (x) (expansion-of-clause x)) or something similar. Looks like a fun idea to explore so I'm wondering if someone's played with something like this before.
(It's even more fun to turn map-like iterators into generators using continuations, but that's fully off-topic. :-))
Cheers, Luís
On Tue, Mar 13, 2018 at 3:08 PM Russ Tyndall <russ@acceleration.net <mailto:russ@acceleration.net>> wrote:
Here is an existing "sampling" clause to pull a random sample from a larger data set. The long and short is just use a finally clause, as you would when writing a normal iterate loop.
(iterate:defmacro-clause (sampling expr &optional into var size size) "resevoir sample the input" (let ((sample (or var iterate::*result-var*))) (alexandria:with-unique-names (i sample-size sigil buffer row) `(progn (with ,sample) (with ,sample-size = (or ,size 100)) (with ,buffer = (make-array ,sample-size :initial-element ',sigil)) (with ,i = 0) (if (< ,i ,sample-size) (setf (aref ,buffer ,i) ,expr) (let ((r (random ,i))) (when (< r ,sample-size) (setf (aref ,buffer r) ,expr)))) (incf ,i) (finally ;; convert our sample to a list, but only if we actually took the sample (when (plusp ,i) (setf ,sample (iter (for ,row in-vector ,buffer) (until (eq ,row ',sigil)) (collect ,row)))))))))
Cheers, Russ Tyndall Acceleration.net
On 03/13/2018 10:49 AM, Robert Goldman wrote:
I was going to define an |AVERAGING| collector clause for iterate, but I'm not sure how to do it. The obvious thing, it seemed to me, would be to sum the values as I go along, and count them, and then divide the sum by the count when leaving the loop.
But the examples for |DEFMACRO-CLAUSE| in the manual do all of their work while iterating, and there doesn't seem to be an "at-end" hook. Is the kind of thing I would like feasible, and if so, how is it to be done?
thanks! r