How to remove an item form an collection atom?

[Ricardo Sanchez]

I'm storing particles in an atom and I would like to remove them from the collection atom once a condition is met, here is my update-particle function:

(defn update-particle

  [{:keys [position velocity age] :as particle}]

  (let [new-position-x (+ (:x position) (:x velocity))

        new-position-y (+ (:y position) (:y velocity))

        new-age (if (> age 0) (dec age) 0)

        new-is-dead (if (= age 0) true false)]

    (println new-is-dead)

    (assoc particle

      :position {:x new-position-x

                 :y new-position-y}

      :age new-age

      :is-dead new-is-dead)))

So the particle slowly die on each frame by decrementing the "age" local variable and when the age reach 0 the "is-dead" property of the particle is updated to "true" and is at that moment when I need to remove the particle from the atom.

Hope that makes sense, any help will be much appreciated

[Nikita Beloglazov]

Hi Ricardo

I think you can remove dead particles like this:

(defn remove-dead [particles]
  (remove :is-dead particles))

(swap! particles-atom remove-dead)

Nikita

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[Ricardo Sanchez]

Hey Nikita,

Plug-and-play it works straight away!

Many thanks

[Ricardo Sanchez]

1 more question, now I have 2 calls to swap! over my particles container atom like this:

(swap! particles-container remove-particles)

(swap! particles-container update-particles)

Is there a way to merge these 2 into a single call over the same atom?

Hope that makes sense

[Nikita Beloglazov]

Check comp function.

--

[Ricardo Sanchez]

Works like a charm! I change it to:

(swap! particles-container (comp update-particles remove-particles))

Thanks again!