Hi all,
I have a sequence of {:key K :value V} maps. There is no guarantee that
there is one map for every known K. I need to ensure that there is a map
for each known K.
Imagine the sequence represents a distribution between 1 and 5. The
initial sequence might only be [{:key 3 :value 30} {:key 4 :value 40}]. I
want it to be [{:key 1 :value nil} {:key 2 :value nil} {:key 3 :value 30}
{:key 4 :value 40} {:key 5 :value nil}].
(There is a sensible reason for {:key K :value V} rather than {K V} by the
way, but it would be possible to temporarily represent the sequence as [K1
V1 K2 V2] and then convert it back.)
In Java I would do something like:
// create a convenient look up to avoid nasty N^2 lookups
Map<Object, Object> keyToValue = new HashMap....
for (Map<Object, Object> kvMap: kvSequence)
keyToValue.put(kvMap.get("key"), kvMap.put("value"));
List<Object> allKeys = calculateAllKeys();
List<Map<Object, Object>> results = new Array....
for (Object key: allKeys)
Object result = keyToValue.get(key); // null is fine for missing keys
results.put(key, result);
return results;
What is the (far more elegant and succinct!) way in Clojure?
My intuition says something like create a map of K/V (i.e. {k1 nil k2 nil})
for all known keys, convert the existing sequence of maps into a flattened
map, merge them together allowing the original sequence to take precedence
and then group them back into [{:key k1 :value v1} {:key k2 :value v2}].
Any hints/clues - is this the right approach?
Thanks a bunch!
Col
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