Best way to loop a map of maps

[Ryan]

Hi all,

I am trying to figure out a better way to loop the following map than using nested doseq. The map has the following structure:

(def m
  {"outerKeyA" {:innerKeyA {"string id" {:foo 1 :bar 2}}}
   "outerKeyB" {:innerKeyB {"string id" {:bar 5 :baz 10}}}})

So, right now i am doing the following:

(doseq [[outer-keys collections] m]
  (doseq [[collection-name collection] collections]
    (doseq [[string-id data] collection]
      ;; do stuff with all the above 
)))

Is there a more idiomatic/better way to do deeply nested iterations/traversal of map of maps?

Thank you for any replies!

Ryan 

[Jay Fields]

I was going to type in the example with multiple bindings, but this
will probably be more helpful:
http://blog.jayfields.com/2013/05/clojure-combining-calls-to-doseq-and-let.html

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[Cedric Greevey]

Tree-seq? But then, if the data is structured so each level has a distinct purpose, that's not really a great fit.

Perhaps we need a for/doseq analog of assoc-in, update-in, etc.?

At the very least I think this might work:

(doseq [[outer-keys collections] m
        [collection-name collection] collections
        [string-id data] collection]

  ;; do stuff with the above
)

[James Ferguson]

`update-in` could be helpful, depending on what exactly you're doing.

(doseq [keyA keys, keyB otherkeys]

  (update-in m [keyA keyB] some-function))

[Ryan]

Thanks guys for the useful answers :)

Ryan

[Jeroen van Dijk]

Don't forget about the option of walking over a map by using clojure.walk/postwalk or clojure.walk/prewalk

I use these functions often lately. Especially useful if you have to update values in your map and they could occur anywhere. It is a bit tricky to get working at first, because the return value of each step needs to match the structure that is currently walked. For that reason you sometimes need to switch between a postwalk instead of a prewalk etc.

Try this for a demo

(def m
  {"outerKeyA" {:innerKeyA {"string id" {:foo 1 :bar 2}}}
   "outerKeyB" {:innerKeyB {"string id" {:bar 5 :baz 10}}}})

(clojure.walk/postwalk-demo m)

[Ryan]

I've seen postwalk and prewalk but never really played around with them so I will give it a shot.

Thanks for your input!

Ryan

[Thomas Heller]

FWIW you can simplify the nested doseqs like this

(doseq [[outer-keys collections] m

            [collection-name collection] collections

            [string-id data] collection]

  ;; do stuff with the above

  )

HTH,

/thomas

[Thomas Heller]

Oh nvm, just saw that it was suggested before.

But maybe this is new:

(def m

  {"outerKeyA" {:innerKeyA {"string id" {:foo 1 :bar 2}}}

   "outerKeyB" {:innerKeyB {"string id" {:bar 5 :baz 10}}}})

(defn nested-seq [m]

  (for [[outer-key collections] m

        [collection-name collection] collections

        [string-id data] collection]

    {:outer-key outer-key :collection-name collection-name :string-id string-id :data data}

    ))

(pprint (nested-seq m))

;; produces

({:outer "outerKeyA",

  :collection-name :innerKeyA,

  :string-id "string id",

  :data {:foo 1, :bar 2}}

 {:outer "outerKeyB",

  :collection-name :innerKeyB,

  :string-id "string id",

  :data {:bar 5, :baz 10}})

for list comprehensions behave like doseq except that they return whatever the body does, thus letting you move your side effects somewhere else.

Maybe this helps,

/thomas

[Ryan]

Thank you for your input Thomas.

All replies have definitely been very useful :)

Cheers,

Ryan