Clojure- filter complex vector

Question

I have been trying to filter complex vector like that

(def mySymbolT [[:name "salary" :type "string" :kind "static" :index 0]
  [:name "money" :type "string" :kind "static" :index 1] 
  [:name "count" :type "int" :kind "field" :index 0]])

My goal is to return the quantity of elements that has the same kind: For example, for kind "static" I expect 2 as an answer. So far I got to write this:

(defn countKind [symbolTable kind]
  (count(map first(filter #(= (:kind %) kind) symbolTable))))

Its not working. I must say that I'm new to Clojure and I dont understand well how filter goes with map, so I will be glad to hear explanations. (Yes, I have read the documentation about map and filter, still explanations missing for me, especially when I try to apply to large vectors.)

Answer 1

Your data would be better expressed as an array of maps than of vectors:

(def your-table [{:name "salary", :type "string", :kind "static", :index 0}
                 {:name "money", :type "string", :kind "static", :index 1} 
                 {:name "count", :type "int", :kind "field", :index 0}])

You can get there from here by ...

(def your-table
  (mapv (partial apply array-map) mySymbolT))

Now we can

• use the keyword :kind as a function to extract those values, and
• the core function frequencies to return what you ask.

For example ...

(frequencies (map :kind your-table))
;{"static" 2, "field" 1}

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By the way, the Clojure idiom is to hyphenate words in a symbol: my-symbol-t instead of mySymbolT.