Thanks for the ideas guys
I especially like the reduce/assoc approach. It's the one most clear
to me so far and also the most efficient one, I guess, as it does only
one assoc per changed key, without creating other intermediate maps.
So this is what I ended up using, with the nice side-effect that I now
also have a reusable function:
(defn map-map
([f map] (map-map f map (keys map)))
([f map keys]
(reduce (fn [m k] (assoc m k (f (m k)))) map keys)))
(map-map inc map keys)
It also happens to be 3 times as fast as my initial implementation,
using that small data set from my first post.
On Jun 18, 2:41 pm, Timothy Pratley <timothyprat...@gmail.com> wrote:
> Your version is already succinct, is there something you particularly
> don't like about it?
>
> I would probabbly write it like this:
> (defn inc-values-in-map
> [map keys]
> (reduce #(assoc %1 %2 (inc (%1 %2 0))) map keys))
> Because it caters better with (inc-values-in-map m
> [:one :three :one :four])
>
> Or more readably:
> (defn assoc-fn
> [f default]
> (fn [m k]
> (assoc m k (f (m k default))))
> (defn inc-values-in-map
> [map keys]
> (reduce (assoc-fn inc 0) map keys))
>
> But its longer than yours :)
>
> On Jun 18, 3:21 pm, Rowdy Rednose <rowdy.redn...@gmx.net> wrote:
>
> > Say I've got this map of keys to integer values:
>
> > (def m {:one 0 :two 0 :three 0})
>
> > I want to write a function "inc-values-in-map" that takes such a map,
> > a collection of keys and will increment those keys' values in the map.
>
> > In other words, calling
>
> > (inc-values-in-map m [:one :three])
>
> > should return
>
> > {:one 1, :two 0, :three 1}
>
> > I've come up with this:
>
> > (defn inc-values-in-map
> > [map keys]
> > (merge-with + map (zipmap keys (repeat 1))))
>
> > Aren't there more elegant ways to implement this function?
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