There are several ways to merge maps in Clojure.
(merge {:a 1} {:b 2})
{:a 1, :b 2}(into {} '({:a 1} {:b 2}))
{:a 1, :b 2}(reduce conj '({:a 1} {:b 2}))
{:a 1, :b 2}into is more efficient than reduce because it uses transient collections.
(apply merge '({:a 1} {:b 2}))
{:a 1, :b 2}If there is a key that is in multiple maps, then the value from the last map will end up in the combined map.
(into {} '({:a 1} {:b 2} {:b 3}))
{:a 1, :b 3}merge-with allows to specify how to combine values for the same keys using a custom function. Here, we are using + function to simply sum up values for the same key.
(merge-with + {:a 1} {:b 2} {:b 3})
{:b 5, :a 1}You can use union from clojure.set to merge sets of elements as shown below.
(use 'clojure.set)
(merge-with union
{:a #{1 2 3}, :b #{4 5 6}}
{:a #{2 3 11 22}, :c #{1 2 3}})
{:a #{1 22 3 2 11}, :b #{4 6 5}, :c #{1 3 2}}