hey Sean -- The ones on the reducers reference page: https://clojure.org/reference/reducers
On Friday, January 25, 2019 at 4:05:12 PM UTC-8, Sean Corfield wrote: > Which docs are you reading? The docstring for r/fold says this – with no > indication of calling (reducef) with no arguments (well, unless you do not > supply combinef – in which case reducef will be used for that, so (reducef) > would be called to seed the reductions): > > > > "Reduces a collection using a (potentially parallel) reduce-combine > > strategy. The collection is partitioned into groups of approximately > > n (default 512), each of which is reduced with reducef (with a seed > > value obtained by calling (combinef) with no arguments). The results > > of these reductions are then reduced with combinef (default > > reducef). combinef must be associative, and, when called with no > > arguments, (combinef) must produce its identity element. These > > operations may be performed in parallel, but the results will > > preserve order." > > > > Sean Corfield -- (970) FOR-SEAN -- (904) 302-SEAN > An Architect's View -- http://corfield.org/ > > "If you're not annoying somebody, you're not really alive." > -- Margaret Atwood > > > > *From: *Brian Craft <javascript:> > *Sent: *Friday, January 25, 2019 3:36 PM > *Subject: *r/fold combinef and reducef init values > > > > From the docs: > > > > r/fold takes a reducible collection and partitions it into groups of > approximately n (default 512) elements. Each group is reduced using the > reducef function. The reducef function will be called with no arguments to > produce an identity value in each partition. The results of those > reductions are then reduced with the combinef (defaults to reducef) > function. When called with no arguments, (combinef) must produce its > identity element - this will be called multiple times. Operations may be > performed in parallel. Results will preserve order. > > > > So, this seems to say r/fold will partition the collection and reduce each > partition using the (reducef) as the init value. > > > > Then, all these intermediate results will be reduced with combinef, using > (combinef) as the init value. > > > > However, in test it seems (reducef) is never called, and (combinef) is > used as the init value for calls to reducef. > > > > (defn combinef > > ([] {:combine :f}) > > ([acc v] acc)) > > > > (defn reducef > > ([] {:reduce :f}) > > ([acc v] > > (println "acc" acc "v" v) > > v)) > > > > (clojure.core.reducers/fold combinef reducef ["foo" "bar"]) > > > > ; outputs: > > acc {:combine :f} v foo > > acc foo v bar > > "bar" > > > > The accumulator in reducef is the init value from combinef, not the init > value from reducef. > > > > What's going on? > > -- > You received this message because you are subscribed to the Google > Groups "Clojure" group. > To post to this group, send email to clo...@googlegroups.com <javascript:> > Note that posts from new members are moderated - please be patient with > your first post. > To unsubscribe from this group, send email to > clojure+u...@googlegroups.com <javascript:> > For more options, visit this group at > http://groups.google.com/group/clojure?hl=en > --- > You received this message because you are subscribed to the Google Groups > "Clojure" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to clojure+u...@googlegroups.com <javascript:>. > For more options, visit https://groups.google.com/d/optout. > > > -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
