This simple solution is symetrical, stores both rows and colums and this
way you get instant access both to any column and row with constant penalty
on get, assoc and update.
It feels a bit messy because you decided to not differentiate between
horizontal and vertical indices. That may be a good choice and give nice
code later, but is somewhat surprising (you must be sure that sets of
horizontal and vertical indices are disjoint).
(defn get2d
([t i] (into (into {} ((first t) i)) ((second t) i)))
([t x y] (if-let [res (get-in (first t) [x y])]
res
(get-in (second t) [x y]))))
(defn assoc2d [[rows cols] [x y] v]
[(assoc-in rows [x y] v) (assoc-in cols [y x] v)])
Your example:
user=> (def foo (-> [] (assoc2d [1 :C] '[x y z]) (assoc2d [2 :A] "2a")
(assoc2d [2 :B] "2b") (assoc2d [3 :A] :3a) (assoc2d [3 :C] "Foo")))
#'user/foo
user=> foo
[{3 {:C "Foo", :A :3a}, 2 {:B "2b", :A "2a"}, 1 {:C [x y z]}}
{:B {2 "2b"}, :A {3 :3a, 2 "2a"}, :C {3 "Foo", 1 [x y z]}}]
user=> (get2d foo :A)
{3 :3a, 2 "2a"}
user=> (get2d foo 2)
{:B "2b", :A "2a"}
user=> (get2d foo :A 2)
"2a"
user=> (get2d foo 2 :A)
"2a"
Please note the double into in get2d. Simple (into ((first t) i) ((second
t) i)) doesn't work as expected when first argument is nil.
To make get2d and assoc2d more consistent one could remove brackets around
[x y] in the argument list of assoc2d.
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