(ns rlm.map-utils

     "A lot of times you want to transform maps by some function

      that operates only on their keys or values, but then get a

      map object back again.  This makes that sort of thing easier."

   ^{:author "Robert McIntyre"}

   (:use [rlm

 	 [dreams :only [defn-decorated]]

 	 [decorators :only [preserve-meta]]]))

 

 

 (defn map-keys

   "Transform a map by applying a function to its keys

    and \"dragging along\" its values.  the transformation

    function must be one-to-one for the keys of the map

    and its range or else the resulting map would have more than

    one value for a key"

   [f m]

   (zipmap (map f (keys m)) (vals m)))

 

 (defn map-vals

   "Transform a map by applying a function to its values, keeping the

    keys the same."

   [f m]

   (zipmap (keys m) (map f (vals m))))

 

 

 (defn filter-keys

   "Makes a new map which contains only pairs for which

    the filter function on the key of the pair returns true."

   [fun m]

   (select-keys m (filter fun (keys m))))

 

 

 (defn filter-vals

   "Makes a new map which contains only pairs for which

    the filter function on the value of the pair returns true."

   [fun m]

     (into {} (filter (comp fun val) m)))

 

 

 (defn sort-map-by

   "returns a new sorted map using the provided function as a comparator

    the comparator function takes two KEYS and compares them"

   [fn map]

   (into (sorted-map-by fn ) map))

 

 (defn def-map

   "takes a map and creates in the current namespace symbols

   corresponding to its keys with values corresponding to its

   values. If the symbols already exist, it just overwrites them.

   Great for debugging at the REPL because you can just define a test

   map, then establish all the key-val variables, then copy snippets

   from a function which references a map in this way and directly test

   the code with those values."

   [])