CODEWITHSUNDEEP
mergeclojure
Rattus
Rattus

Reputation: 105

Clojure: Combine hash-maps only if key is in both maps?

I have two hash maps and am trying to merge them together while only keeping the keys found in both maps.
Ex:

{a true, b true, c true, d true, e true}
merged with {c true, d true, e true, f true}
would yield {c true, d true, e true}

I am pretty new to Clojure and just can't seem to figure out how to do this. Thanks

Upvotes: 2

Views: 331

Answers (2)

tap
tap

Reputation: 414

Apart from select-keys, min-key is also useful. This function can be used with an arbitrary number of map

(defn min-merge [& ms]
  (let [min-keys (keys (apply min-key count ms))]
    (select-keys (apply merge ms) min-keys)))

Try

user=> (min-merge {:a 1 :b 2} {:a 3} {:a 4 :b 5 :c 6})
{:a 4}

Upvotes: 1

fl00r
fl00r

Reputation: 83680

There is a select-keys function in the standard library

(let [a {:a true :b true :c true :d true :e true}
      b {:c true :d true :e true :f true}
      b-keys (keys b)]
  (select-keys a b-keys))
#=> {:c true, :d true, :e true}

Upvotes: 7

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