Is there an easy way in Clojure (maybe using specter) to filter collections depending on whether the an arbitrarily nested key with a known name contains an element ?
Ex. :
(def coll [{:res [{:a [{:thekey [
"the value I am looking for"
...
]
}
]}
{:res ...}
{:res ...}
]}])
Knowing that :a could have a different name, and that :thekey could be nested somewhere else.
Let's say I would like to do :
#(find-nested :thekey #{"the value I am looking for"} coll) ;; returns a vector containing the first element in coll (and maybe others)
use zippers.
in repl:
user> coll
[{:res [{:a [{:thekey ["the value I am looking for"]}]} {:res 1} {:res 1}]}]
user> (require '[clojure.zip :as z])
nil
user> (def cc (z/zipper coll? seq nil coll))
#'user/cc
user> (loop [x cc]
(if (= (z/node x) :thekey)
(z/node (z/next x))
(recur (z/next x))))
["the value I am looking for"]
update:
this version is flawed, since it doesn't care about :thekey being the key in a map, or just keyword in a vector, so it would give unneeded result for coll [[:thekey [1 2 3]]]. Here is an updated version:
(defn lookup-key [k coll]
(let [coll-zip (z/zipper coll? #(if (map? %) (vals %) %) nil coll)]
(loop [x coll-zip]
(when-not (z/end? x)
(if-let [v (-> x z/node k)] v (recur (z/next x)))))))
in repl:
user> (lookup-key :thekey coll)
["the value I am looking for"]
user> (lookup-key :absent coll)
nil
lets say we have the same keyword somewhere in a vector in a coll:
(def coll [{:res [:thekey
{:a [{:thekey ["the value I am looking for"]}]}
{:res 1} {:res 1}]}])
#'user/coll
user> (lookup-key :thekey coll)
["the value I am looking for"]
which is what we need.
Related
There is a map containing sequences. The sequences contain items.
I want to remove a given item from any sequence that contains it.
The solution I found does what it should, but I wonder if there is a better
or more elegant way to achieve the same.
my current solution:
(defn remove-item-from-map-value [my-map item]
(apply merge (for [[k v] my-map] {k (remove #(= item %) v)})))
The test describe the expected behaviour:
(require '[clojure.test :as t])
(def my-map {:keyOne ["itemOne"]
:keyTwo ["itemTwo" "itemThree"]
:keyThree ["itemFour" "itemFive" "itemSix"]})
(defn remove-item-from-map-value [my-map item]
(apply merge (for [[k v] my-map] {k (remove #(= item %) v)})))
(t/is (= (remove-item-from-map-value my-map "unknown-item") my-map))
(t/is (= (remove-item-from-map-value my-map "itemFive") {:keyOne ["itemOne"]
:keyTwo ["itemTwo" "itemThree"]
:keyThree ["itemFour" "itemSix"]}))
(t/is (= (remove-item-from-map-value my-map "itemThree") {:keyOne ["itemOne"]
:keyTwo ["itemTwo"]
:keyThree ["itemFour" "itemFive" "itemSix"]}))
(t/is (= (remove-item-from-map-value my-map "itemOne") {:keyOne []
:keyTwo ["itemTwo" "itemThree"]
:keyThree ["itemFour" "itemFive" "itemSix"]}))
I'm fairly new to clojure and am interested in different solutions.
So any input is welcome.
I throw in the specter
version for good measure. It keeps the vectors inside the map
and it's really compact.
(setval [MAP-VALS ALL #{"itemFive"}] NONE my-map)
Example
user=> (use 'com.rpl.specter)
nil
user=> (def my-map {:keyOne ["itemOne"]
#_=> :keyTwo ["itemTwo" "itemThree"]
#_=> :keyThree ["itemFour" "itemFive" "itemSix"]})
#_=>
#'user/my-map
user=> (setval [MAP-VALS ALL #{"itemFive"}] NONE my-map)
{:keyOne ["itemOne"],
:keyThree ["itemFour" "itemSix"],
:keyTwo ["itemTwo" "itemThree"]}
user=> (setval [MAP-VALS ALL #{"unknown"}] NONE my-map)
{:keyOne ["itemOne"],
:keyThree ["itemFour" "itemFive" "itemSix"],
:keyTwo ["itemTwo" "itemThree"]}
i would go with something like this:
user> (defn remove-item [my-map item]
(into {}
(map (fn [[k v]] [k (remove #{item} v)]))
my-map))
#'user/remove-item
user> (remove-item my-map "itemFour")
;;=> {:keyOne ("itemOne"),
;; :keyTwo ("itemTwo" "itemThree"),
;; :keyThree ("itemFive" "itemSix")}
you could also make up a handy function map-val performing mapping on map values:
(defn map-val [f data]
(reduce-kv
(fn [acc k v] (assoc acc k (f v)))
{} data))
or shortly like this:
(defn map-val [f data]
(reduce #(update % %2 f) data (keys data)))
user> (map-val inc {:a 1 :b 2})
;;=> {:a 2, :b 3}
(defn remove-item [my-map item]
(map-val (partial remove #{item}) my-map))
user> (remove-item my-map "itemFour")
;;=> {:keyOne ("itemOne"),
;; :keyTwo ("itemTwo" "itemThree"),
;; :keyThree ("itemFive" "itemSix")}
I think your solution is mostly okay, but I would try to avoid the apply merge part, as you can easily recreate a map from a sequence with into. Also, you could also use map instead of for which I think is a little bit more idiomatic in this case as you don't use any of the list comprehension features of for.
(defn remove-item-from-map-value [m item]
(->> m
(map (fn [[k vs]]
{k (remove #(= item %) vs)}))
(into {})))
Another solution much like #leetwinski:
(defn remove-item [m i]
(zipmap (keys m)
(map (fn [v] (remove #(= % i) v))
(vals m))))
Here's a one-liner which does this in an elegant way. The perfect function for me to use in this scenario is clojure.walk/prewalk. What this fn does is it traverse all of the sub-forms of the form that you pass to it and it transforms them with the provided fn:
(defn remove-item-from-map-value [data item]
(clojure.walk/prewalk #(if (map-entry? %) [(first %) (remove #{item} (second %))] %) data))
What the remove-item-from-map-value fn will do is it will check if current form is a map entry and if so, it will remove specified key from its value (second element of the map entry, which is a vector containing a key and a value, respectively).
The best this about this approach is that is is completely extendable: you could decide to do different things for different types of forms, you can also handle nested forms, etc.
It took me some time to master this fn but once I got it I found it extremely useful!
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.
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 []])))))
I have a function that returns the indexes in seq s at which value v exists:
(defn indexes-of [v s]
(map first (filter #(= v (last %)) (zipmap (range) s))))
What I'd like to do is extend this to apply any arbitrary function for the existence test. My idea is to use a multimethod, but I'm not sure exactly how to detect a function. I want to do this:
(defmulti indexes-of ???)
(defmethod indexes-of ??? [v s] ;; v is a function
(map first (filter v (zipmap (range) s))))
(defmethod indexes-of ??? [v s] ;; v is not a function
(indexes-of #(= v %) s))
Is a multimethod the way to go here? If so, how can I accomplish what I'm trying to do?
If you want to use a multimethod it should be on the filter function, which is the one changing according to the existence test type.
So
(defmulti filter-test (fn [value element]
(cond
(fn? value) :function
:else :value)))
(defmethod filter-test :function
[value element]
(apply value [element]))
(defmethod filter-test :value
[value element]
(= value element))
(defn indexes-of [v s]
(map first (filter #(filter-test v (last %)) (zipmap (range) s))))
Consider the JVM doesn't support first-class functions, or lambdas, out of the box, so there's no "function" data type to dispatch on, that's the reason the fn? test.
None the less the predicate solution proposed by noisesmith is the proper way to go in this situation IMO.
(defmulti indexes-of (fn [v _]
(if (fn? v)
:function
:value)))
(defmethod indexes-of :function
[f coll]
(keep-indexed (fn [i v] (when (f v) i)) coll))
(defmethod indexes-of :value
[v coll]
(indexes-of (partial = v) coll))
How about something simpler and more general:
(defn index-matches [predicate s]
(map first (filter (comp predicate second) (map vector (range) s))))
user> (index-matches even? (reverse (range 10)))
(1 3 5 7 9)
user> (index-matches #{3} [0 1 2 3 1 3 44 3 1 3])
(3 5 7 9)
thanks to a suggestion from lgrapenthin, this function is also now effective for lazy input:
user> (take 1 (index-matches #{300000} (range)))
(300000)
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))