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1 (ns rlm.map-utils
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2 "A lot of times you want to transform maps by some function
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3 that operates only on their keys or values, but then get a
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4 map object back again. This makes that sort of thing easier."
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5 ^{:author "Robert McIntyre"}
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6 (:use [rlm
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7 [dreams :only [defn-decorated]]
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8 [decorators :only [preserve-meta]]]))
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9
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10
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11 (defn map-keys
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12 "Transform a map by applying a function to its keys
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13 and \"dragging along\" its values. the transformation
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14 function must be one-to-one for the keys of the map
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15 and its range or else the resulting map would have more than
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16 one value for a key"
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17 [f m]
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18 (zipmap (map f (keys m)) (vals m)))
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19
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20 (defn map-vals
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21 "Transform a map by applying a function to its values, keeping the
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22 keys the same."
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23 [f m]
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24 (zipmap (keys m) (map f (vals m))))
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25
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26
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27 (defn filter-keys
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28 "Makes a new map which contains only pairs for which
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29 the filter function on the key of the pair returns true."
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30 [fun m]
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31 (select-keys m (filter fun (keys m))))
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32
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33
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34 (defn filter-vals
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35 "Makes a new map which contains only pairs for which
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36 the filter function on the value of the pair returns true."
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37 [fun m]
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38 (into {} (filter (comp fun val) m)))
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39
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40
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41 (defn sort-map-by
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42 "returns a new sorted map using the provided function as a comparator
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43 the comparator function takes two KEYS and compares them"
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44 [fn map]
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45 (into (sorted-map-by fn ) map))
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46
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47 (defn def-map
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48 "takes a map and creates in the current namespace symbols
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49 corresponding to its keys with values corresponding to its
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50 values. If the symbols already exist, it just overwrites them.
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51 Great for debugging at the REPL because you can just define a test
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52 map, then establish all the key-val variables, then copy snippets
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53 from a function which references a map in this way and directly test
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54 the code with those values."
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55 [])
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