Is there a standard function transforming a map's vals

[samppi]

Is there a function in the standard libraries that's equivalent to
this:

(defn transform-map [pred a-map]
(into {} (map (comp pred val) a-map)))

(is (= {:a 4, :b 3}
(transform-map inc {:a 3, :b 2})))

It's not like I can't write this myself; I use this a lot, though, and
I'm wondering if it's somewhere in the core or contrib. (I searched,
but I couldn't find it, either.)

[Sean Devlin]

The short answer is no.

This came up on the dev list here:

http://groups.google.com/group/clojure-dev/browse_thread/thread/4b20e40d83095c67#

Oh, and I'd write the function slightly differently

(defn transform-map [f a-map] ...)

The f implies a mapping operation. pred implies a filter operation.

[samppi]

Oops, you're right; I was thinking about something else. And I have
another mistake in my function too—I meant:

(defn transform-map [f a-map]
(into {} (map #(vector (key %) (f (val %))) a-map)))

It's unfortunate that it's not in any standard library yet. I've used
this function in every single Clojure program that I've written. Ah,
well.

On Oct 10, 8:48 pm, Sean Devlin <francoisdev...@gmail.com> wrote:
> The short answer is no.
>
> This came up on the dev list here:
>

> http://groups.google.com/group/clojure-dev/browse_thread/thread/4b20e...

[Daniel Werner]

On Oct 11, 6:02 am, samppi <rbysam...@gmail.com> wrote:
> Oops, you're right; I was thinking about something else. And I have
> another mistake in my function too—I meant:
>
> (defn transform-map [f a-map]
> (into {} (map #(vector (key %) (f (val %))) a-map)))
>
> It's unfortunate that it's not in any standard library yet. I've used
> this function in every single Clojure program that I've written. Ah,
> well.

Konrad Hinsen's generic functor multimethod seems to do exactly what
you want:

user=> (use 'clojure.contrib.generic.functor)
nil
user=> (fmap inc {:a 4, :b 3})
{:a 5, :b 4}

Actually it is not limited to maps:

user=> (fmap inc [4 3])
[5 4]

It's just too easy to miss beautiful and useful gems like this in the
depths of clojure.contrib.

[Stuart Sierra]

On Oct 10, 8:40 pm, samppi <rbysam...@gmail.com> wrote:

> (defn transform-map [f a-map]
> (into {} (map #(vector (key %) (f (val %))) a-map)))

I always find map transformations easier to write with reduce:

(defn transform-map [f mm]
(reduce (fn [m [k v]] (assoc m k (f v))) {} mm))

-SS

[John Harrop]

Agreed. That's why I may create a kind of "mind map" of that library (and throw in clojure.core) that can find functions by, well, function. So all the stuff for manipulating maps can be found, or all the stuff for file I/O, etc. 

[Christophe Grand]

Note that if you're only interested in using the resulting map as a function, (comp f map) works well (you can throw memoize in for good measure).

--
Professional: http://cgrand.net/ (fr)
On Clojure: http://clj-me.blogspot.com/ (en)