1.1 --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
     1.2 +++ b/src/rlm/map_utils.clj	Tue Oct 18 00:57:08 2011 -0700
     1.3 @@ -0,0 +1,55 @@
     1.4 +(ns rlm.map-utils
     1.5 +    "A lot of times you want to transform maps by some function
     1.6 +     that operates only on their keys or values, but then get a
     1.7 +     map object back again.  This makes that sort of thing easier."
     1.8 +  ^{:author "Robert McIntyre"}
     1.9 +  (:use [rlm
    1.10 +	 [dreams :only [defn-decorated]]
    1.11 +	 [decorators :only [preserve-meta]]]))
    1.12 +
    1.13 +
    1.14 +(defn map-keys
    1.15 +  "Transform a map by applying a function to its keys
    1.16 +   and \"dragging along\" its values.  the transformation
    1.17 +   function must be one-to-one for the keys of the map
    1.18 +   and its range or else the resulting map would have more than
    1.19 +   one value for a key"
    1.20 +  [f m]
    1.21 +  (zipmap (map f (keys m)) (vals m)))
    1.22 +
    1.23 +(defn map-vals
    1.24 +  "Transform a map by applying a function to its values, keeping the
    1.25 +   keys the same."
    1.26 +  [f m]
    1.27 +  (zipmap (keys m) (map f (vals m))))
    1.28 +
    1.29 +
    1.30 +(defn filter-keys
    1.31 +  "Makes a new map which contains only pairs for which
    1.32 +   the filter function on the key of the pair returns true."
    1.33 +  [fun m]
    1.34 +  (select-keys m (filter fun (keys m))))
    1.35 +
    1.36 +
    1.37 +(defn filter-vals
    1.38 +  "Makes a new map which contains only pairs for which
    1.39 +   the filter function on the value of the pair returns true."
    1.40 +  [fun m]
    1.41 +    (into {} (filter (comp fun val) m)))
    1.42 +
    1.43 +
    1.44 +(defn sort-map-by
    1.45 +  "returns a new sorted map using the provided function as a comparator
    1.46 +   the comparator function takes two KEYS and compares them"
    1.47 +  [fn map]
    1.48 +  (into (sorted-map-by fn ) map))
    1.49 +
    1.50 +(defn def-map
    1.51 +  "takes a map and creates in the current namespace symbols
    1.52 +  corresponding to its keys with values corresponding to its
    1.53 +  values. If the symbols already exist, it just overwrites them.
    1.54 +  Great for debugging at the REPL because you can just define a test
    1.55 +  map, then establish all the key-val variables, then copy snippets
    1.56 +  from a function which references a map in this way and directly test
    1.57 +  the code with those values."
    1.58 +  [])