CODEWITHSUNDEEP
clojure
Rob Buhler
Rob Buhler

Reputation: 2511

clojure set of maps - basic filtering

Clojure beginner here..

If I have a set of maps, such as 

 (def kids #{{:name "Noah" :age 5}
     {:name "George":age 3}
     {:name "Reagan" :age 1.5}})

I know I can get names like this

  (map :name kids)

1) How do I select a specific map? For example I want to get back the map where name="Reagan".

 {:name "Reagan" :age 1.5}

Can this be done using a filter?

2) How about returning the name where age = 3?

Upvotes: 4

Views: 521

Answers (2)

Michał Marczyk
Michał Marczyk

Reputation: 84331

There's clojure.set/select:

(clojure.set/select set-of-maps #(-> % :age (= 3)))

And similarly with name and "Reagan". The return value in this case will be a set.

You could also use filter without any special preparations, since filter calls seq on its collection argument (edit: as already described by ffriend while I was typing this):

(filter #(-> % :age (= 3))) set-of-maps)

Here the return value will be a lazy seq.

If you know there will only be one item satisfying your predicate in the set, some will be more efficient (as it will not process any additional elements after finding the match):

(some #(if (-> % :age (= 3)) %) set-of-maps)

The return value here will be the matching element.

Upvotes: 6

ffriend
ffriend

Reputation: 28492

Yes, you can do it with filter:

(filter #(= (:name %) "Reagan") kids)

(filter #(= (:age %) 3) kids)

Upvotes: 8

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