In Clojure, how can I find the value of a key that may be deep in a nested map structure? For example:
(def m {:a {:b "b"
:c "c"
:d {:e "e"
:f "f"}}})
(find-nested m :f)
=> "f"
Clojure offers tree-seq to do a depth-first traversal of any value. This will simplify the logic needed to find your nested key:
(defn find-nested
[m k]
(->> (tree-seq map? vals m)
(filter map?)
(some k)))
(find-nested {:a {:b {:c 1}, :d 2}} :c)
;; => 1
Also, finding all matches becomes a matter of replacing some with keep:
(defn find-all-nested
[m k]
(->> (tree-seq map? vals m)
(filter map?)
(keep k)))
(find-all-nested {:a {:b {:c 1}, :c 2}} :c)
;; => [2 1]
Note that maps with nil values might require some special treatment.
Update: If you look at the code above, you can see that k can actually be a function which offers a lot more possibilities:
to find a string key:
(find-nested m #(get % "k"))
to find multiple keys:
(find-nested m #(some % [:a :b]))
to find only positive values in maps of integers:
(find-nested m #(when (some-> % :k pos?) (:k %)))
If you know the nested path then use get-in.
=> (get-in m [:a :d :f])
=> "f"
See here for details: https://clojuredocs.org/clojure.core/get-in
If you don't know the path in your nested structure you could write a function that recurses through the nested map looking for the particular key in question and either returns its value when it finds the first one or returns all the values for :f in a seq.
If you know the "path", consider using get-in:
(get-in m [:a :d :f]) ; => "f"
If the "path" is unknown you can use something like next function:
(defn find-in [m k]
(if (map? m)
(let [v (m k)]
(->> m
vals
(map #(find-in % k)) ; Search in "child" maps
(cons v) ; Add result from current level
(filter (complement nil?))
first))))
(find-in m :f) ; "f"
(find-in m :d) ; {:e "e", :f "f"}
Note: given function will find only the first occurrence.
Here is a version that will find the key without knowing the path to it. If there are multiple matching keys, only one will be returned:
(defn find-key [m k]
(loop [m' m]
(when (seq m')
(if-let [v (get m' k)]
v
(recur (reduce merge
(map (fn [[_ v]]
(when (map? v) v))
m')))))))
If you require all values you can use:
(defn merge-map-vals [m]
(reduce (partial merge-with vector)
(map (fn [[_ v]]
(when (map? v) v))
m)))
(defn find-key [m k]
(flatten
(nfirst
(drop-while first
(iterate (fn [[m' acc]]
(if (seq m')
(if-let [v (get m' k)]
[(merge-map-vals m') (conj acc v)]
[(merge-map-vals m') acc])
[nil acc]))
[m []])))))
Related
I have an edn in which I have nested maps. I found one very good example for this Clojure: a function that search for a val in a nested hashmap and returns the sequence of keys in which the val is contained
(def coll
{:a "aa"
:b {:d "dd"
:e {:f {:h "hh"
:i "ii"}
:g "hh"}}
:c "cc"})
With this answer
(defn find-in [coll x]
(some
(fn [[k v]]
(cond (= v x) [k]
(map? v) (if-let [r (find-in v x)]
(into [k] r))))
coll))
My problem is that because of some I can't get a path for every result, only for the first logical truth. I tried map an keep but they break the recursion. How could I make this code to give back path to all of its results, not only the first one? Any help is appreciated.
You can use a helper function to turn a nested map into a flat map with fully qualified keys. Then find-in can just filter on the value and returns the matched keys.
(defn flatten-map [path m]
(if (map? m)
(mapcat (fn [[k v]] (flatten-map (conj path k) v)) m)
[[path m]]))
(defn find-in [coll x]
(->> (flatten-map [] coll)
(filter (fn [[_ v]] (= v x)))
(map first)))
With your sample:
(find-in coll "hh")
=>
([:b :e :f :h] [:b :e :g])
filter gives all of the results, where some will only give you the first result, or nil if there aren't any. Oftentimes the same problem can be solved by filtering then taking the first, rather than using some.
Is there a convenient way in ClojureScript to pretty print a nested hash-map in the way that the whole tree-structure becomes immediately visible.
For instance a map like this
(def my-map {:a {:b 1 :c 9} :b {:d 8 :e {:f 2 :g 3 :h 4}} :c 10})
should be printed like this:
{:a {:b 1
:c 9}
:b {:d 8
:e {:f 2
:g 3
:h 4}}
:c 10}
EDIT: There might also be vectors in the map. The usecase is just to inspect larger data structures during development.
There is no built-in way to do it. You might come close to what you want by using cljs.pprint and setting cljs.pprint/*print-right-margin* to a low value.
I would recommend to take a look at a small library shodan which provides a very useful inspect function:
(require '[shodan.inspection :refer [inspect]])
(inspect {:aaaaaa 1
:bbbbbb {:ccc 2
:dddddd [1 2 3 4 5]}})
It won't print anything in your CLJS REPL but will provide a handy view in your browser's console:
You can collapse and expand nested datastructures - it basically does what you asked for.
As a personal challenge I wrote the following code:
(enable-console-print!)
(def atomic? (complement coll?))
(def padding #(apply str (repeat % " ")))
(def tabulate #(apply str (repeat % "\t")))
(def strcat #(->> (apply concat %&) (apply str)))
(defn my-max-key [x] (if (empty? x) [""] (apply (partial max-key count) x)))
(defn longest-key [m] (->> m keys (filter atomic?) (map str) my-max-key))
(def length (comp count str))
(def not-map? (complement map?))
(def nested? #(some coll? %))
(def join #(apply str (interpose % %2)))
(def join-lines (partial join "\n"))
(defn has-atomic? [coll] (some atomic? coll))
(defn diff-key-lengths [key1 key2] (- (length key1) (length key2)))
(defn convert
([thing] (convert -1 thing))
([depth thing]
(defn convert-items []
(defn convert-seq []
(conj []
(map (partial convert (inc depth)) thing)
""))
(defn string-horizontally [[key value]]
(str (tabulate (inc depth))
key
(padding (diff-key-lengths (longest-key thing) key))
" → "
value))
(defn string-vertically [[key value]]
(str (convert (inc depth) key) "\n"
(convert (+ 2 depth) "↓") "\n"
(convert (inc depth) value) "\n"))
(defn convert-kv [[key value]]
(if (nested? [key value])
(string-vertically [key value])
(string-horizontally [key value])))
(cond (atomic? thing)
[(str (tabulate depth) thing)]
(not-map? thing)
(convert-seq)
(map? thing)
(map convert-kv thing)))
(->> (convert-items) flatten join-lines)))
(def sample-input [["the first thing in this nested vector"]
{{"this is a key in a nested map"
"that points to me!!!"}
{"and that entire map points to this map!!!"
"cool!!!"
"but it gets cooler cause..."
"the value's line up!!!"}}])
(->> sample-input convert println)
The terminal output is (psst... the values in a map do line up but I don't think that chrome uses a monospaced font!):
Say we have a collection containing a nested data structure:
(def coll
{:a "aa"
:b {:d "dd"
:e {:f {:h "hh"
:i "ii"}
:g "gg"}}
:c "cc"})
I would like to create a function that search for a val anywhere in the nested structure and returns the sequence of keys in which the val is contained
(search-parents "gg" coll) ; or (search-parents coll "gg")
;> [:b :e :g]
Thanks!
As far as I can tell, there's no built-in function that does this. It seems like you're essentially looking for an inverse of clojure.core/get-in. I thinking clojure.walk might be useful here, but I don't think this is a very good fit.
However, it's pretty straightforward to code up a recursive function to do the search and only return matching keys:
(defn find-in [coll x]
(some
(fn [[k v]]
(cond (= v x) [k]
(map? v) (if-let [r (find-in v x)]
(into [k] r))))
coll))
I had a need to expand it to cover also a vector of maps:
(defn find-in [coll x]
(some
(fn [[k v]]
(cond (= v x) [k]
(map? v) (if-let [r (find-in v x)]
(into [k] r))
(vector? v) (let [v1 (mapv #(find-in % x) v)]
(if-let [r (some #(when % %) v1)]
(let [i (.indexOf v1 r)]
(into (into [k] [i]) r))
))))
coll))
I'm looking to write a function that is similar to assoc-in but removes keys instead of adding it:
(dissoc-in {:a {:b 0}} [:a :b])
;;=> {:a {}}
I got up to here:
(def m {:a {:b {:c 1}}})
(assoc m :a (assoc (:a m) :b (dissoc (:b (:a m)) :c)))
;;=> {:a {:b {}}}
but the whole nested thing is messing with my head
I write this using update-in:
(update-in {:a {:b 0 :c 1}} [:a] dissoc :b)
=>
{:a {:c 1}}
How about:
(defn dissoc-in
"Dissociates an entry from a nested associative structure returning a new
nested structure. keys is a sequence of keys. Any empty maps that result
will not be present in the new structure."
[m [k & ks :as keys]]
(if ks
(if-let [nextmap (get m k)]
(let [newmap (dissoc-in nextmap ks)]
(if (seq newmap)
(assoc m k newmap)
(dissoc m k)))
m)
(dissoc m k)))
Example:
(dissoc-in {:a {:b 0 :c 1}} [:a :b])
Result:
{:a {:c 1}}
dissoc-in was once part of clojure.contrib.core, and is now part of core.incubator.
If you want to keep empty maps, you can alter the code slightly:
(defn dissoc-in
[m [k & ks :as keys]]
(if ks
(if-let [nextmap (get m k)]
(let [newmap (dissoc-in nextmap ks)]
(assoc m k newmap))
m)
(dissoc m k)))
Example:
(dissoc-in {:a {:b {:c 0}}} [:a :b])
Result:
{:a {}}
Here is a general solution based on update-in:
(defn dissoc-in [m p]
(if (get-in m p)
(update-in m
(take (dec (count p)) p)
dissoc (last p))
m))
Being inspired by Dominic's code. I wrote a more succinct version
(defn dissoc-in
[m [k & ks]]
(if-not ks
(dissoc m k)
(assoc m k (dissoc-in (m k) ks))))
(dissoc-in {:a {:b {:c 1}}} [:a :b :c]) ;; => {:a {:b {}}}
Another version dissoc-in2 recursively removes empty maps
(defn dissoc-in2
[m [k & ks]]
(if-not ks
(dissoc m k)
(let [nm (dissoc-in2 (m k) ks)]
(cond (empty? nm) (dissoc m k)
:else (assoc m k nm)))))
(ut/dissoc-in {:a {:b {:c 3}}} [:a :b :c])
;;; => {:a {:b {}}}
(ut/dissoc-in2 {:a {:b {:c 3}}} [:a :b :c])
;;=> {}
No need to write one, clojure.core.incubator already has a dissoc-in:
=> (dissoc-in {:children [{:name "Billy" :age 5}]} [:children 0 :age])
{:children [{:name "Billy"}]}
I'd recommend using dissoc-in from the medley library.
Here is the code as of version 0.7.0:
(defn dissoc-in
"Dissociate a value in a nested assocative structure, identified by a sequence
of keys. Any collections left empty by the operation will be dissociated from
their containing structures."
[m ks]
(if-let [[k & ks] (seq ks)]
(if (seq ks)
(let [v (dissoc-in (get m k) ks)]
(if (empty? v)
(dissoc m k)
(assoc m k v)))
(dissoc m k))
m))
Here's a link to the source code of dissoc-in in medley master.
(defn dissoc-in [m ks]
(let [parent-path (butlast ks)
leaf-key (last ks)]
(if (= (count ks) 1)
(dissoc m leaf-key)
(update-in m parent-path dissoc leaf-key))))
Very simple + silly question:
Does clojure provide multi maps? I currently have something like this:
(defn wrap [func]
(fn [mp x]
(let [k (func x)]
(assoc mp k
(match (get mp k)
nil [x]
v (cons v x))))))
(defn create-mm [func lst]
(reduce (wrap func) {} lst))
Which ends up creating a map, where for each key, we have a vector of all elements with that key. However, it seems like multi maps is a very basic data structure, and I wonder if clojure has it built-in.
Thanks
I don't think this is really necessary as a distinct type, as Clojure's flexibility allow you to quickly make your own by just using maps and sets. See here:
http://paste.lisp.org/display/89840
Edit (I should have just pasted this in since it's so small)
Example Code (Courtesy Stuart Sierra)
(ns #^{:doc "A multimap is a map that permits multiple values for each
key. In Clojure we can represent a multimap as a map with sets as
values."}
multimap
(:use [clojure.set :only (union)]))
(defn add
"Adds key-value pairs the multimap."
([mm k v]
(assoc mm k (conj (get mm k #{}) v)))
([mm k v & kvs]
(apply add (add mm k v) kvs)))
(defn del
"Removes key-value pairs from the multimap."
([mm k v]
(let [mmv (disj (get mm k) v)]
(if (seq mmv)
(assoc mm k mmv)
(dissoc mm k))))
([mm k v & kvs]
(apply del (del mm k v) kvs)))
(defn mm-merge
"Merges the multimaps, taking the union of values."
[& mms]
(apply (partial merge-with union) mms))
(comment
(def mm (add {} :foo 1 :foo 2 :foo 3))
;; mm == {:foo #{1 2 3}}
(mm-merge mm (add {} :foo 4 :bar 2))
;;=> {:bar #{2}, :foo #{1 2 3 4}}
(del mm :foo 2)
;;=> {:foo #{1 3}}
)
Extra test for the case pointed out in the comments:
(comment
(-> {} (add :a 1) (del :a 1) (contains? :a))
;;=> false
)