Lazy group-by for sorted maps?

[Colin Yates]

Is there such a thing as a lazy group-by for a sequence of elements when the elements are sorted on the criteria used to group them?  I can imagine how one would look in a few lines of Clojure code but I am surprised there isn't one already.

My actual criteria is that I am pulling things from a database that live on the "many" side of a one-many and I want to sort on the "one" FK.

This is all based on the assumption that http://clojuredocs.org/clojure_core/clojure.core/group-by is eager!

[Jonah Benton]

Sounds like a job for partition-by:

http://clojuredocs.org/clojure_core/clojure.core/partition-by

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[Colin Yates]

Great - thanks!

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[Michael-Keith Bernard (SegFaultAX)]

For the partition-by solution to work, you have to ensure that the result set from the query is sorted by the foreign key:

(partition-by identity "aaabbbcccaaabbbcc")
;;=> ((\a \a \a) (\b \b \b) (\c \c \c) (\a \a \a) (\b \b \b) (\c \c))
(partition-by identity (sort "aaabbbcccaaabbbcc"))
;;=> ((\a \a \a \a \a \a) (\b \b \b \b \b \b) (\c \c \c \c \c))

[Colin Yates]

Yep, sure.  Thanks.