Thank you very much. I had the feeling I should reduce over the tree-path,
but was not able to come up with something good like you did.
Best Regards,
Sven
Am Dienstag, 24. März 2015 22:58:18 UTC+1 schrieb Francis Avila:
>
> Notice that get-in-via is simply reduce:
>
> (defn get-in-via [m via ks]
> (reduce (fn [m' k] (via m' k)) m ks))
>
>
> Same as:
>
> (defn get-in-via [m via ks]
> (reduce via m ks))
>
>
>
> Same as:
>
> (reduce via m ks)
>
>
>
> So once you write your "step" function, traversal is taken care of by the
> reduction.
>
> On Tuesday, March 24, 2015 at 4:55:23 PM UTC-5, Francis Avila wrote:
>>
>> 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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