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With Maps of Mapsλ︎

Define a collection of star-wars characters using a map of maps. Each character should have an name that they are typically referred to, along with their fullname and skill

(def star-wars-characters
   {:luke   {:fullname "Luke Skywalker" :skill "Targeting Swamp Rats"}
    :vader  {:fullname "Darth Vader"    :skill "Crank phone calls"}
    :jarjar {:fullname "JarJar Binks"   :skill "Upsetting a generation of fans"}})

Now we can refer to the characters using keywords. Using the get function we return all the information about Luke

(get star-wars-characters :luke)

By wrapping the get function around our first, we can get a specific piece of information about Luke

(get (get star-wars-characters :luke) :fullname)

There is also the get-in function that makes the syntax a little easier to read

(get-in star-wars-characters [:luke :fullname])
(get-in star-wars-characters [:vader :fullname])

Or you can get really concise by just talking to the map directly

(star-wars-characters :luke)
(:fullname (:luke star-wars-characters))
(:skill (:luke star-wars-characters))

(star-wars-characters :vader)
(:skill (:vader star-wars-characters))
(:fullname (:vader star-wars-characters))

And finally we can also use the threading macro to minimise our code further

(-> star-wars-characters

(-> star-wars-characters

(-> star-wars-characters

Create a slightly data structure holding data around several developer events. Each event should have a website address, event type, number of attendees, call for papers.


(def dev-event-details
  {:devoxxuk     {:URL                 ""
                  :event-type          "Conference"
                  :number-of-attendees 700
                  :call-for-papers     "open"}
   :hackthetower {:URL                 ""
                  :event-type          "hackday"
                  :number-of-attendees 99
                  :call-for-papers     "closed"}})

This data structure is just a map, with each key being the unique name of the developer event.

The details of each event (the value to go with the event name key) is itself a map as there are several pieces of data associated with each event name. So we have a map where each value is itself a map.

Call the data structure and see what it evaluates too, it should not be a surprise


We can ask for the value of a specific key, and just that value is returned

(dev-event-details :devoxxuk)

In our example, the value returned from the :devoxxuk key is also a map, so we can ask for a specific part of that map value by again using its key

(:URL (dev-event-details :devoxxuk))