The following works but feels/seems wrong. Is there a better way?
dev:cljs.user=> (def x (atom {:v true}))
#'cljs.user/x
dev:cljs.user=> (swap! x assoc-in [:v] (not (:v #x)))
{:v false}
dev:cljs.user=> (swap! x assoc-in [:v] (not (:v #x)))
{:v true}
cljs.user=> (def x (atom {:v true}))
#'cljs.user/x
cljs.user=> (swap! x update :v not)
{:v false}
cljs.user=> #x
{:v false}
(let [a (atom {:v true})]
(swap! a update-in [:v] not)
#a)
=> {:v false}
or you can use specter:
(transform [ATOM :v] not a)
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 a collection of maps
(def a '({:id 9345 :value 3 :type "orange"}
{:id 2945 :value 2 :type "orange"}
{:id 145 :value 3 :type "orange"}
{:id 2745 :value 6 :type "apple"}
{:id 2345 :value 6 :type "apple"}))
I want to group this first by value, followed by type.
My output should look like:
{
:orange [{
:value 3,
:id [9345, 145]
}, {
:value 2,
:id [2935]
}],
:apple [{
:value 6,
:id [2745, 2345]
}]
}
How would I do this in Clojure? Appreciate your answers.
Thanks!
Edit:
Here is what I had so far:
(defn by-type-key [data]
(group-by #(get % "type") data))
(reduce-kv
(fn [m k v] (assoc m k (reduce-kv
(fn [sm sk sv] (assoc sm sk (into [] (map #(:id %) sv))))
{}
(group-by :value (map #(dissoc % :type) v)))))
{}
(by-type-key a))
Output:
=> {"orange" {3 [9345 145], 2 [2945]}, "apple" {6 [2745 2345], 3 [125]}}
I just couldnt figure out how to proceed next...
Your requirements are a bit inconsistent (or rather irregular) - you use :type values as keywords in the result, but the rest of the keywords are carried through. Maybe that's what you must do to satisfy some external formats - otherwise you need to either use the same approach as with :type through, or add a new keyword to the result, like :group or :rows and keep the original keywords intact. I will assume the former approach for the moment (but see below, I will get to the shape as you want it,) so the final shape of data is like
{:orange
{:3 [9345 145],
:2 [2945]},
:apple
{:6 [2745 2345]}
}
There is more than one way of getting there, here's the gist of one:
(group-by (juxt :type :value) a)
The result:
{["orange" 3] [{:id 9345, :value 3, :type "orange"} {:id 145, :value 3, :type "orange"}],
["orange" 2] [{:id 2945, :value 2, :type "orange"}],
["apple" 6] [{:id 2745, :value 6, :type "apple"} {:id 2345, :value 6, :type "apple"}]}
Now all rows in your collection are grouped by the keys you need. From this, you can go and get the shape you want, say to get to the shape above you can do
(reduce
(fn [m [k v]]
(let [ks (map (comp keyword str) k)]
(assoc-in m ks
(map :id v))))
{}
(group-by (juxt :type :value) a))
The basic idea is to get the rows grouped by the key sequence (and that's what group-by and juxt do,) and then combine reduce and assoc-in or update-in to beat the result into place.
To get exactly the shape you described:
(reduce
(fn [m [k v]]
(let [type (keyword (first k))
value (second k)
ids (map :id v)]
(update-in m [type]
#(conj % {:value value :id ids}))))
{}
(group-by (juxt :type :value) a))
It's a bit noisy, and it might be harder to see the forest for the trees - that's why I simplified the shape, to highlight the main idea. The more regular your shapes are, the shorter and more regular your functions become - so if you have control over it, try to make it simpler for you.
I would do the transform in two stages (using reduce):
the first to collect the values
the second for formating
The following code solves your problem:
(def a '({:id 9345 :value 3 :type "orange"}
{:id 2945 :value 2 :type "orange"}
{:id 145 :value 3 :type "orange"}
{:id 2745 :value 6 :type "apple"}
{:id 2345 :value 6 :type "apple"}))
(defn standardise [m]
(->> m
;; first stage
(reduce (fn [out {:keys [type value id]}]
(update-in out [type value] (fnil #(conj % id) [])))
{})
;; second stage
(reduce-kv (fn [out k v]
(assoc out (keyword k)
(reduce-kv (fn [out value id]
(conj out {:value value
:id id}))
[]
v)))
{})))
(standardise a)
;; => {:orange [{:value 3, :id [9345 145]}
;; {:value 2, :id [2945]}],
;; :apple [{:value 6, :id [2745 2345]}]}
the output of the first stage is:
(reduce (fn [out {:keys [type value id]}]
(update-in out [type value] (fnil #(conj % id) [])))
{}
a)
;;=> {"orange" {3 [9345 145], 2 [2945]}, "apple" {6 [2745 2345]}}
You may wish to use the built-in function group-by. See http://clojuredocs.org/clojure.core/group-by
I want to create a map based on variable inputs where a key should only be present if its corresponding value is not nil.
Here's a toy example I came up with:
(defn make-map
[foo bar baz]
(-> {}
(into (and foo {:foo foo}))
(into (and bar {:bar bar}))
(into (and baz {:baz baz}))))
Is there a more accepted/idiomatic way to do this?
I think something like this is a bit more straightforward
(defn make-map
[foo bar baz]
(reduce (fn [m [k v]] (if (some? v) (assoc m k v) m))
{}
{:foo foo :bar bar :baz baz}))
user> (make-map 1 nil 2)
{:baz 2, :foo 1}
user> (make-map nil 1 2)
{:baz 2, :bar 1}
user> (make-map true false true)
{:baz true, :bar false, :foo true}
This uses cond-> to simplify things a little.
(defn make-map
[foo bar baz]
(cond-> {}
foo (assoc :foo foo)
bar (assoc :bar bar)
baz (assoc :baz baz)))
It's hard to tell with the toy example whether there's a better option for you.
(defn make-map [foo bar baz]
(into {}
(filter
#(if-not (nil? (second %)) { (first %) (second %)})
(map vector [ :foo :bar :baz] [for bar baz]))
)
)
For a little bit of variety, a generalisation using for:
(defn some-map
[& args]
(->> (for [[k v] (partition 2 args)
:when (some? v)]
[k v])
(into {})))
Usage:
(some-map :a 1 :b 2 :c nil :d false)
;; => {:a 1, :b 2, :d false}
Or, akin to #noisesmith's answer, something to be applied to an existing map:
(defn some-map
[m]
(into {} (filter (comp some? val) m)))
(some-map {:a 1 :b 2 :c nil :d false})
;; => {:b 2, :d false, :a 1}
You could abstract this to use a syntax and application similar to zipmap so you can have variable argument lists for both keys and args
(defn when-zip
[keys args]
(->> args
(map vector keys)
(remove (comp not second))
(into {})))
(when-zip [:foo :bar :baz :qux] [true nil false 1])
=> {:qux 1, :foo true}
When you don't like the creation of intermediate lazy results you can use Clojure 1.7's transducers or blatantly rip off zipmap's source
(defn when-zip
"Returns a map with each of the keys mapped to
the corresponding val when val is truthy."
[keys vals]
(loop [map {}
ks (seq keys)
vs (seq vals)]
(if (and ks vs)
(recur (if-let [v (first vs)]
(assoc map (first ks) v)
map)
(next ks)
(next vs))
map)))
(when-zip [:foo :bar :baz :qux] [true nil false 1])
=> {:qux 1, :foo true}
If you really still need the original syntax you could then use this to define specific versions
(defn make-map
[& args]
(when-zip [:foo :bar :baz :qux] args))
(make-map true nil false 1)
=> {:qux 1, :foo true}
On the other hand, you could just not bother with removing nils and use zipmap; when you do a map lookup on a non-existing key further on, it will give the same result as a key with value nil anyway:
(:baz {:qux 1, :foo true})
=> nil
(:baz {:qux 1, :baz nil, :bar false :foo true})
=> nil
Of course, this is different with :bar. But usually it's better to do nil and false punning at the consuming stage instead of during transformation.
Just for completeness, here's something closer to what I was trying to reach for originally but didn't quite get.
(defn make-map
[foo bar baz]
(apply hash-map
(concat
(and foo [:foo foo])
(and bar [:bar bar])
(and baz [:baz baz]))))
Suppose I have a map:
{:name "foo"
:age "bar"}
And another one
{:name (fn [val] (println val))
:age (fn [val] (= val "bar"))}
I want to apply function keyed by :name on second map to the first map, which also keyed by :name and the function keyed by :age to the first map which keyed by :age. How to do this the clojure way?
You can use merge-with
(def m1 {:name "foo"
:age "bar"})
(def m2 {:name (fn [val] (println val))
:age (fn [val] (= val "bar"))})
user=> (merge-with #(%1 %2) m2 m1)
foo
{:name nil, :age true}
map over one map and get corresponding function from the other one.
(def m1 {:name "foo"
:age "bar"})
(def m2 {:name (fn [val] (println val))
:age (fn [val] (= val "bar"))})
(map (fn [[k v]]
((get m2 k) v))
m1)
Each iteration over the map passes a vector to the function, in your sample:
[:name "foo"]
[:age "bar"]
So destructuring the function parameter into [[k v]] gives you each key/value separately.
(def data { :name "don knotts"
:dob "1/1/1940"
:cob "Valdosta" })
(def fxns {:name identity :dob identity :cob clojure.string/reverse})
(defn bmap [data fxn]
(apply merge (for [[k1 d] data [k2 f] fxn :when (= k1 k2)]
{k1 (f d)})))
;=user>{:cob "atsodlaV", :dob "1/1/1940", :name "don knotts"}
I like this, if you need more resilience:
(defn fmm [m fm]
(let [f (fn [k] ((get fm k identity) (k m)))
ks (keys m)]
(zipmap ks (map f ks))))
I'm having trouble finding solution to the following problem:
Lets say I have a map:
(def defaults {
:name "John"
:surname "Doe"
:info {:date-of-birth "01-01-1980"
:registered [{:type "newsletter" :name "breaking news" }]}
})
And then I pass a similar structured map but I want to conjoin the vectors and overwrite the rest of the keys:
(def new {
:name "Peter"
:info {:date-of-birth "11-01-1986"
:registered [{:type "alert" :name "mobile-alert" }]}
})
And I want this result:
{:name "Peter"
:surname "Doe"
:info {:date-of-birth "11-01-1986"
:registered [{:type "newsletter" :name "breaking news" }
{:type "alert" :name "mobile-alert" }]}}
Now I can do this easily by using static syntax like:
(reduce conj (get-in defaults [:info :registered]) (get-in new [:info :registered]))
(There is probably a better way...) But I was hoping more of a dynamic function with the following properties:
Keep all keys from both maps, without knowing the structure
Update any keys with the values from the right map
if the val of a key is a vector, then conj the vector with the vector of the right map (if the appropriate key exists of course)
Thanks for the help in advance :)
You should definitely look at merge-with function. This is possible implementation:
(defn deep-merge [a b]
(merge-with (fn [x y]
(cond (map? y) (deep-merge x y)
(vector? y) (concat x y)
:else y))
a b))
Here's a possible implementation for this kind of functionality. It is at least a starting point, you may need some extra validations depending on the possible structure of your data (e.g. what if the overriding map's value is a vector but the value in the default map is not even a collection?).
(declare merge-maps)
(defn merge-map [x [k v]]
(cond (vector? v)
(assoc x k (vec (reduce conj (x k) v)))
(map? v)
(assoc x k (merge-maps (x k) v))
:esle
(assoc x k v)))
(defn merge-maps [x y]
(reduce merge-map x y))
(merge-maps defaults new)
;= {:info {:date-of-birth "11-01-1986",
;= :registered [{:name "breaking news", :type "newsletter"}
;= {:name "mobile-alert", :type "alert"}]},
;= :name "Peter",
;= :surname "Doe"}