clojure.core/get-in

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Type: function Added: Clojure 1.2 Examples: 8 Runnable: 5

([m ks] [m ks not-found])

Returns the value in a nested associative structure, where ks is a sequence of keys. Returns nil if the key is not present, or the not-found value if supplied.

Examples

by tomoj on 2010-07-24 . May have evaluation errors. ▶

;; We can use get-in for reaching into nested maps: (def m {:username "sally" :profile {:name "Sally Clojurian" :address {:city "Austin" :state "TX"}}}) #'user/m (get-in m [:profile :name]) "Sally Clojurian" (get-in m [:profile :address :city]) "Austin" (get-in m [:profile :address :zip-code]) nil (get-in m [:profile :address :zip-code] "no zip code!") "no zip code!" ;; Vectors are also associative: (def v [[1 2 3] [4 5 6] [7 8 9]]) #'user/v (get-in v [0 2]) 3 (get-in v [2 1]) 8 ;; We can mix associative types: (def mv {:username "jimmy" :pets [{:name "Rex" :type :dog} {:name "Sniffles" :type :hamster}]}) #'user/mv (get-in mv [:pets 1 :type]) :hamster

by octopusgrabbus on 2012-04-20 . May have evaluation errors. ▶

(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")

by fitswell on 2013-08-26 ▶

;; spam link removed

by phreed on 2014-10-02 ▶

;; Introduction of references is jarring to get-in usage (def owners [{:owner "Jimmy" :pets (ref [{:name "Rex" :type :dog} {:name "Sniffles" :type :hamster}])} {:owner "Jacky" :pets (ref [{:name "Spot" :type :mink} {:name "Puff" :type :magic-dragon}])}]) ;;=> 'user/owners (get-in owners [0 :pets]) ;;=> #<Ref@: [{:name "Rex", :type :dog} {:name "Sniffles", :type :hamster}> ;; In order to go deeper the get needs to be split ;; as the deref cannot be used as part of the get. (-> (get-in owners [0 :pets]) deref (get-in [1 :type])) ;;=> :hamster ;; At this point it clear that the thread operator ;; can be used to produce similar results. (-> owners (nth 0) :pets deref (nth 1) :type) ;;=> :hamster

by huahaiy on 2014-11-16 ▶

;; If the nested structure contains list, it does not work, because list is ;; not an associative structure. (def a {:a '({:b1 2} {:b2 4}) :c 3}) ;;=> 'user/a (get-in a [:a 0 :b1]) ;;=> nil ;; However, if the nested structure contains a vector then it does work. (def a1 {:a [{:b1 2} {:b2 4}] :c 3}) ;; => 'user/a1 (get-in a1 [:a 0 :b1]) ;; => 2

by titonbarua on 2017-12-28 ▶

;; If an empty sequence is used as keys, the whole structure is returned. (get-in {:a 1 :b 2} []) ;;=> {:a 1, :b 2} (get-in {:a 1, :b 2} '()) ;;=> {:a 1, :b 2} ;; nil also counts as an empty sequence! (get-in {:a 1 :b 2} nil) ;;=> {:a 1, :b 2} ;; Be careful if you use a nill-able key sequence with not-found value. ;; This can be a source of bug. (get-in {:a 1 :b 2} nil :nothing) ;;=> {:a 1, :b 2}

by ibercode on 2018-02-10 ▶

;;practical example (def employee {:name "John" :details {:email "info@domain.com" :phone "555-144-300"}}) (get-in employee [:details :email]) ;;"info@domain.com"

by MicahElliott on 2020-10-06 . May have evaluation errors. ▶

;; Difference between nil values vs non-existing keys, and default values ;; In this case, we don't know what will be the `:b` in our map, ;; so attempting to guard with a 0 default value. (pos? (get-in {:a {:b 42}} [:a :b] 0)) ;=> 42 -> true (as expected) (pos? (get-in {:a nil} [:a :b] 0)) ;=> 0 -> false, no key (as expected) (pos? (get-in {:a {:b nil}} [:a :b] 0)) ;=> nil -> NPE (misleading code) (pos? (or (get-in {:a {:b nil}} [:a :b]) 0)) ;=> false (works but ugly) ;; Better to use `some->` for such situations (some-> {:a {:b nil}} :a :b pos?) ;=> nil (YAY!) (some-> {:a {}} :a :b pos?) ;=> nil (some-> {:a {:b 42}} :a :b pos?) ;=> true

See also

• clojure.core/assoc-in (7)
• clojure.core/update-in (10)
• clojure.core/find (2)
• clojure.core/get (8)
• clojure.core/-> (4)
• clojure.core/some-> (0)

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