How to use assoc-in to update multiple values in a map? (Clojure)

Question

I am trying to update every line that has an "enjoy-clojure?" that returns true "sanity-rating" to -2 (i.e johnny's sanity-rating would be updated to -2)

(def student-database
  { 0 {:enjoy-clojure? false, :name "jimmy",:sanity-rating 9}
    1 { :enjoy-clojure? true, :name "johnny",:sanity-rating 2}
    2 { :enjoy-clojure? true, :name "jilly",:sanity-rating 5}
    3 { :enjoy-clojure? true, :name "janey",:sanity-rating 8}
    4 {:enjoy-clojure? false, :name "jelly",:sanity-rating 10}}) 

I am new to Clojure and have tried researching update and assoc and can't really seem to find a way to update multiple elements ((assoc student-database [0 :sanity-rating] -2) only returns updates one element). To filter student-database to take out the student's who returned true I have

(defn unhinged?
 [record]
 (:enjoy-clojure? record))

(defn minus-two-students
 [student-database]
 (filter #(unhinged? %)
  (map student-database [0 1 2 3 4])))

And returns

({:enjoy-clojure? true, :name "johnny", :sanity-rating 2} {:enjoy-clojure? 
   true, :name "jilly", :sanity-rating 5} {:enjoy-clojure? true, :name 
   "janey", :sanity-rating 8})

Which works great but I also need it to update all their sanity-rating to -2. Any helps/tips would be much appreciated.

Answer 1

Here comes the reduce-kv version!

(defn adjust-sanity [student]
  (if (:enjoy-clojure? student)
    (assoc student :sanity-rating -2)
    student))

(reduce-kv (fn [m k v] (assoc m k (adjust-sanity v)))
           {}
           student-database)
=>
{0 {:enjoy-clojure? false, :name "jimmy", :sanity-rating 9},
 1 {:enjoy-clojure? true, :name "johnny", :sanity-rating -2},
 2 {:enjoy-clojure? true, :name "jilly", :sanity-rating -2},
 3 {:enjoy-clojure? true, :name "janey", :sanity-rating -2},
 4 {:enjoy-clojure? false, :name "jelly", :sanity-rating 10}}

Or another option with a helper function to update all a map's values:

(defn update-vals [m f]
  (reduce-kv (fn [m' k v] (assoc m' k (f v))) {} m))
(update-vals student-database adjust-sanity)

Answer 2

You didn't say in your question that you want the function to returns only (= enjoy-clojure? true) records, but from your comments in the other answers, I feel that's what you really want.

So maybe this?

(defn unhinged?
  [record]
  (:enjoy-clojure? record))

(defn minus-two-students
  [student-database]
  (->> student-database
       vals
       (filter unhinged?)
       (map #(assoc % :sanity-rating -2))))

Output will be

({:enjoy-clojure? true, :name "johnny", :sanity-rating -2} 
 {:enjoy-clojure? true, :name "jilly", :sanity-rating -2} 
 {:enjoy-clojure? true, :name "janey", :sanity-rating -2})

Answer 3

To update the entire db, you could do:

(def student-database
  {0 {:enjoy-clojure? false, :name "jimmy",:sanity-rating 9}
   1 { :enjoy-clojure? true, :name "johnny",:sanity-rating 2}
   2 { :enjoy-clojure? true, :name "jilly",:sanity-rating 5}
   3 { :enjoy-clojure? true, :name "janey",:sanity-rating 8}
   4 {:enjoy-clojure? false, :name "jelly",:sanity-rating 10}})

(defn update-db [db]
  (zipmap (keys db)
          (map (fn [student]
                 (cond-> student
                   (:enjoy-clojure? student)
                   (assoc :sanity-rating -2)))
               (vals db))))

(update-db student-database) ;;=> 
{0 {:enjoy-clojure? false, :name "jimmy", :sanity-rating 9}, 
 1 {:enjoy-clojure? true, :name "johnny", :sanity-rating -2} ...}

Answer 4

the simplest would be like this:

(reduce-kv (fn [acc idx row]
             (assoc acc idx
                    (if (:enjoy-clojure? row)
                      (assoc row :sanity-rating -2)
                      row)))
           {}
           student-database)

;;=> {0 {:enjoy-clojure? false, :name "jimmy", :sanity-rating 9}, 
;;    1 {:enjoy-clojure? true, :name "johnny", :sanity-rating -2}, 
;;    2 {:enjoy-clojure? true, :name "jilly", :sanity-rating -2}, 
;;    3 {:enjoy-clojure? true, :name "janey", :sanity-rating -2}, 
;;    4 {:enjoy-clojure? false, :name "jelly", :sanity-rating 10}}

you can also do something like this:

(reduce-kv (fn [res k {ec? :enjoy-clojure?}]
             (if ec?
               (assoc-in res [k :sanity-rating] -2)
               res))
           student-database
           student-database)

;;=> {0 {:enjoy-clojure? false, :name "jimmy", :sanity-rating 9}, 
;;    1 {:enjoy-clojure? true, :name "johnny", :sanity-rating -2}, 
;;    2 {:enjoy-clojure? true, :name "jilly", :sanity-rating -2}, 
;;    3 {:enjoy-clojure? true, :name "janey", :sanity-rating -2}, 
;;    4 {:enjoy-clojure? false, :name "jelly", :sanity-rating 10}}