Ep 051: Maps! Maps! Maps!

Functional Design in Clojure

Each week, we discuss a different topic about Clojure and functional programming.

If you have a question you'd like us to discuss, tweet @clojuredesign, send an email to [email protected], or join the #clojuredesign-podcast channel on the Clojurians Slack.

This week, our topic is: "Maps! Maps! Maps!" We discuss maps and their useful features, including a key distinction that we couldn't live without.

Selected quotes:

• "Working with Clojure makes you feel like you're living in the future!"
• "Maps are bags of dimensions."

• "The namespace of the key is the entity, the name is the attribute, and the value is the value."

• "Flatter maps make it so you end up writing less code."

Related episodes:

• Time Log series:
  • 015: Finding the Time
  • 016: When 8 - 1 = 6
  • 017: Data, at Your Service
  • 018: Did I Work Late on Tuesday?
  • 019: Dazed by Weak Weeks
  • 020: Data Dessert
• 049: Keywords! Keywords! Keywords!

Links:

• Love Letter To Clojure (Part 1) - Gene Kim

Code sample:

;; Player records: one nested, one with rich keys.  (def players-nested  [{:player {:id 123  :name "Russell"  :position :point-guard}  :team {:id 432  :name "Durham Denizens"  :division :eastern}}  {:player {:id 124  :name "Frank"  :position :midfield}  :team {:id 432  :name "Durham Denizens"  :division :eastern}}])  (def players-rich  [{:player/id 123  :player/name "Russell"  :player/position :point-guard  :team/id 432  :team/name "Durham Denizens"  :team/division :eastern}  {:player/id 124  :player/name "Frank"  :player/position :midfield  :team/id 432  :team/name "Durham Denizens"  :team/division :eastern}])   ;; Extract player and team id, along with team name  ; Nested (defn extract  [player]  (let [{:keys [player team]} player]  {:player (select-keys player [:id])  :team (select-keys team [:id :name])}))  #_(map extract players-nested) ; ({:player {:id 123}, :team {:id 432, :name "Durham Denizens"}} ; {:player {:id 124}, :team {:id 432, :name "Durham Denizens"}})  ; Rich #_(map #(select-keys % [:player/id :team/id :team/name]) players-rich) ; ({:player/id 123, :team/id 432, :team/name "Durham Denizens"} ; {:player/id 124, :team/id 432, :team/name "Durham Denizens"})   ;; Sort by team name and then player name  ; Nested #_(sort-by (juxt #(-> % :team :name) #(-> % :player :name)) players-nested) ; ({:player {:id 124, :name "Frank", :position :midfield}, ; :team {:id 432, :name "Durham Denizens", :division :eastern}} ; {:player {:id 123, :name "Russell", :position :point-guard}, ; :team {:id 432, :name "Durham Denizens", :division :eastern}})  ; Rich #_(sort-by (juxt :team/name :player/name) players-rich) ; ({:player/id 124, ; :player/name "Frank", ; :player/position :midfield, ; :team/id 432, ; :team/name "Durham Denizens", ; :team/division :eastern} ; {:player/id 123, ; :player/name "Russell", ; :player/position :point-guard, ; :team/id 432, ; :team/name "Durham Denizens", ; :team/division :eastern})