Returns the value in a nested associative structure,
where ks is a sequence of ke(ys. Returns nil if the key is not present,
or the not-found value if supplied.
;; We can use get-in for reaching into nested maps:
user=> (def m {:username "sally"
:profile {:name "Sally Clojurian"
:address {:city "Austin" :state "TX"}}})
#'user/m
user=> (get-in m [:profile :name])
"Sally Clojurian"
user=> (get-in m [:profile :address :city])
"Austin"
user=> (get-in m [:profile :address :zip-code])
nil
user=> (get-in m [:profile :address :zip-code] "no zip code!")
"no zip code!"
;; Vectors are also associative:
user=> (def v [[1 2 3]
[4 5 6]
[7 8 9]])
#'user/v
user=> (get-in v [0 2])
3
user=> (get-in v [2 1])
8
;; We can mix associative types:
user=> (def mv {:username "jimmy"
:pets [{:name "Rex"
:type :dog}
{:name "Sniffles"
:type :hamster}]})
#'user/mv
user=> (get-in mv [:pets 1 :type])
:hamster
(def s1 [[:000-00-0000 "TYPE 1" "JACKSON" "FRED"]
[:000-00-0001 "TYPE 2" "SIMPSON" "HOMER"]
[:000-00-0002 "TYPE 4" "SMITH" "SUSAN"]])
(def cols [0 2 3])
(defn f1
[s1 col]
(map #(get-in s1 [% col] nil) (range (count s1))))
(apply interleave (map (partial f1 s1) cols))
(:000-00-0000 "JACKSON" "FRED" :000-00-0001 "SIMPSON" "HOMER" :000-00-0002 "SMITH" "SUSAN")
Source
clojure/core.clj:4921
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(defn get-in
"Returns the value in a nested associative structure,
where ks is a sequence of ke(ys. Returns nil if the key is not present,
or the not-found value if supplied."
{:added "1.2"}
([m ks]
(reduce get m ks))
([m ks not-found]
(loop [sentinel (Object.)
m m
ks (seq ks)]
(if ks
(let [m (get m (first ks) sentinel)]
(if (identical? sentinel m)
not-found
(recur sentinel m (next ks))))
m))))
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