Separate out traversal from selection to make this clearer.
We make a generic traversal function get-in-via. It accepts a via function
which takes the current result and some value which determines the next
result, and returns the next result.
(defn get-in-via [m via ks]
(reduce (fn [m' k] (via m' k)) m ks))
Here is a via function that follows folder paths. This is a single "step"
of the reduction.
(defn via-folderpath [items foldername]
(->> items
(filter #(and (= (:type %) :folder)
(= (:name %) foldername)))
(first)
:children))
Example of use:
(get-in-via ffs via-folderpath ["sub2" "sub21"])
;=> [{:name "lein-env", :type :file}]
On Tuesday, March 24, 2015 at 4:22:21 PM UTC-5, Sven Richter wrote:
>
> Hi,
>
> I wrote a function to trackdown a path in a vector containing nested maps:
>
> (defn get-files-from-folder-path [ffs folder-path]
> (filter #(= :file (:type %))
> (loop [tree-path-position 0 acc [] fof ffs]
> (let [folder (first (filter #(and
> (= :folder (:type %))
> (= (nth folder-path
> tree-path-position nil) (:name %))) fof))]
> (if (not (:children folder))
> acc
> (recur (inc tree-path-position)
> (if (= (+ tree-path-position 1) (count folder-path))
> (concat acc (:children folder)) acc)
> (:children folder)))))))
>
> And these are the inputs:
> (def ffs [{:type :folder, :name "sub1", :children [{:type :file, :name
> "datomic-data.edn"}]}
> {:type :folder, :name "sub2", :children [{:type :file, :name "foo
> (1).csv"}
> {:type :folder, :name
> "sub21", :children [{:type :file, :name "lein-env"}]}]}])
>
> (def tree-path ["sub2" "sub21"])
>
> And I call it like this:
>
> (get-files-from-folder-path ffs tree-path)
>
> Is there a way to use reduce for that? I was stuck because I think I have to
> reduce on two lists here,
> but reduce only takes one to start with, thats why I chose the loop / recur
> route. Which works
> but it looks ugly to me and I am afraid in one week I want understand it
> anymore.
>
> Thanks Regards,
> Sven
>
>
>
>
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