Dear Steve,
I’m new in clojure as well, but if we try to break up your one function into
two, we’d have the following:
(defn update1
"Given a two-level nested vector of maps, two keys for each map, and
an update function. Apply the function in the inner map, and returns
nested structure."
[vect [k1 k2] f]
(map
(fn [m] (update-in m [k1] update2 k2 f))
vect))
(defn update2
"Given a vector of maps, a key for the map, and an update function.
Apply the function to value of the key."
[vect k f]
(map
(fn [item] (update-in item [k] f))
vect))
which seems easier to follow than one, though YMMV.
Best,
--
jv
Sent with Sparrow (http://www.sparrowmailapp.com/?sig)
On Monday, December 22, 2014 at 12:34 PM, Steve Ashton wrote:
> I'm trying to figure out if there is a better / more concise / more generic
> way to write an update function. The data I have is a vector of maps
> containing vectors of maps.
> For example:
> [{:values [{:y 1 :x 4}{:y 2 :x 7}]}{:values [{:y 5 :x 8}]}]
>
> The goal is to update all the :y values or all the :x values according to a
> passed-in function. As a concrete example, I'd like to invert the sign of all
> the :y values.
>
> So here's the working function which I've come up with:
>
> (defn update-nested-fields
> "Updates a vector of maps containing vectors of maps"
> [col [k1 k2] f]
> (map (fn [outer-map]
> (update-in outer-map
> [k1]
> (fn [inner-col]
> (map
> (fn [inner-map]
> (update-in inner-map [k2] f))
> inner-col))))
> col))
>
>
> ;; invert the :y values
> (update-nested-fields
> [{:values [{:y 1 :x 4}{:y 2 :x 7}]}{:values [{:y 5 :x 8}]}]
> [:values :y]
> (partial * -1))
>
>
>
> As you can see, at a simple level it is: (map (update-in (map (update-in f))).
>
> I'm really wondering if I'm missing an obvious simplification. I've tried to
> decide if a threading macro would help, but I don't see how, since the outer
> collection is provided to the outermost map function, rather than the
> inner-most function.
>
>
>
>
>
>
>
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