Details
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Type:
Enhancement
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Status:
Open
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Priority:
Minor
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Resolution: Unresolved
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Affects Version/s: None
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Fix Version/s: None
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Component/s: None
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Labels:
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Patch:Code
Description
clojure.data/diff, on line 118, defines:
java.util.Map (diff-similar [a b] (diff-associative a b (set/union (keys a) (keys b))))
Since keys returns a key seq, this seems like an error. clojure.set/union has strange and inconsistent behavior with regard to non-sets, and in this case the two key seqs are concatenated. Based on a cursory benchmark, it seems that this bug 
is a slight performance gain when the maps have no common keys, and a significant performance loss when the maps have the same keys. The results are still correct because of the merging reduce in diff-associative.
The patch is easy (just call set on each key seq).
clj-1087-diff-perf-enhance-patch-v1.txt dated Oct 15 2012 implements Tom's suggested performance enhancement, although not exactly in the way he suggested. It does calculate the union of the two key sequences.