Clojure: Convert hash-maps key strings to keywords?

Question

I'm pulling data from Redis using Aleph:

(apply hash-map @(@r [:hgetall (key-medication id)]))

The problem is this data comes back with strings for keys, for ex:

({"name" "Tylenol", "how" "instructions"})

When I need it to be:

({:name "Tylenol", :how "instructions})

I was previously creating a new map via:

{ :name (m "name"), :how (m "how")}

But this is inefficient for a large amount of keys.

If there a function that does this? Or do I have to loop through each?

Answer 1

You can also use the clojure.walk library to achieve the desired result with the function keywordize-keys

(use 'clojure.walk)
(keywordize-keys {"name" "Tylenol", "how" "instructions"})
;=> {:name "Tylenol", :how "instructions"}

This will walk the map recursively as well so it will "keywordize" keys in nested map too

http://clojuredocs.org/clojure_core/clojure.walk/keywordize-keys

Answer 2

There is a handy function called keyword that converts Strings into the appropriate keywords:

(keyword "foo")
=> :foo

So it's just a case of transforming all the keys in your map using this function.

I'd probably use a list comprehension with destructuring to do this, something like:

(into {} 
  (for [[k v] my-map] 
    [(keyword k) v]))

Answer 3

I agree with djhworld, clojure.walk/keywordize-keys is what you want.

It's worth peeking at the source code of clojure.walk/keywordize-keys:

(defn keywordize-keys
  "Recursively transforms all map keys from strings to keywords."
  [m]
  (let [f (fn [[k v]] (if (string? k) [(keyword k) v] [k v]))]
    (clojure.walk/postwalk (fn [x] (if (map? x) (into {} (map f x)) x)) m)))

The inverse transform is sometimes handy for java interop:

(defn stringify-keys
  "Recursively transforms all map keys from keywords to strings."
  [m]
  (let [f (fn [[k v]] (if (keyword? k) [(name k) v] [k v]))]
    (clojure.walk/postwalk (fn [x] (if (map? x) (into {} (map f x)) x)) m)))

Answer 4

Perhaps it is worth noting that, if the incoming data is json and you are using clojure.data.json, you can specify both a key-fn and a value-fn for manipulating results on parsing the string (docs) -

;; Examples from the docs

(ns example
  (:require [clojure.data.json :as json]))


(json/read-str "{\"a\":1,\"b\":2}" :key-fn keyword) 
;;=> {:a 1, :b 2}

(json/read-str "{\"a\":1,\"b\":2}" :key-fn #(keyword "com.example" %))
;;=> {:com.example/a 1, :com.example/b 2}