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Merge pull request #741 from github/finer-grained-rejection-of-candidate-matches

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Finer grained rejection of candidate matches
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Rob Rix 2016-08-19 14:39:50 -04:00 committed by GitHub
commit 0b51a64799
1 changed files with 11 additions and 4 deletions
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15
src/Data/RandomWalkSimilarity.hs
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@ -48,25 +48,32 @@ rws compare as bs
kdbs = KdTree.build (Vector.toList . feature) fbs
featurize index term = UnmappedTerm index (getField (extract term)) term
toMap = IntMap.fromList . fmap (termIndex &&& identity)
-- | Construct a diff for a term in B by matching it against the most similar eligible term in A (if any), marking both as ineligible for future matches.
findNearestNeighbourTo :: UnmappedTerm (Cofree f (Record fields)) -> State (Int, IntMap (UnmappedTerm (Cofree f (Record fields))), IntMap (UnmappedTerm (Cofree f (Record fields)))) (Int, Free (CofreeF f (Both (Record fields))) (Patch (Cofree f (Record fields))))
findNearestNeighbourTo kv@(UnmappedTerm j _ b) = do
(previous, unmappedA, unmappedB) <- get
fromMaybe (insertion previous unmappedA unmappedB kv) $ do
foundA@(UnmappedTerm i _ a) <- nearestUnmapped unmappedA kdas kv
foundA@(UnmappedTerm i _ a) <- nearestUnmapped (IntMap.filterWithKey (\ k _ -> isInMoveBounds previous k) unmappedA) kdas kv
UnmappedTerm j' _ _ <- nearestUnmapped unmappedB kdbs foundA
guard (j == j')
guard (previous <= i && i <= previous + defaultMoveBound)
compared <- compare a b
pure $! do
put (i, IntMap.delete i unmappedA, IntMap.delete j unmappedB)
pure (i, compared)
-- | Determines whether an index is in-bounds for a move given the most recently matched index.
isInMoveBounds previous i = previous <= i && i <= previous + defaultMoveBound
-- | Finds the most-similar unmapped term to the passed-in term, if any.
--
-- RWS can produce false positives in the case of e.g. hash collisions. Therefore, we find the _l_ nearest candidates, filter out any which have already been mapped, and select the minimum of the remaining by (a constant-time approximation of) edit distance.
--
-- cf §4.2 of RWS-Diff
nearestUnmapped :: IntMap (UnmappedTerm (Cofree f (Record fields))) -> KdTree.KdTree Double (UnmappedTerm (Cofree f (Record fields))) -> UnmappedTerm (Cofree f (Record fields)) -> Maybe (UnmappedTerm (Cofree f (Record fields)))
nearestUnmapped
:: IntMap (UnmappedTerm (Cofree f (Record fields))) -- ^ A set of terms eligible for matching against.
-> KdTree.KdTree Double (UnmappedTerm (Cofree f (Record fields))) -- ^ The k-d tree to look up nearest neighbours within.
-> UnmappedTerm (Cofree f (Record fields)) -- ^ The term to find the nearest neighbour to.
-> Maybe (UnmappedTerm (Cofree f (Record fields))) -- ^ The most similar unmapped term, if any.
nearestUnmapped unmapped tree key = getFirst $ foldMap (First . Just) (sortOn (maybe maxBound (editDistanceUpTo defaultM) . compare (term key) . term) (toList (IntMap.intersection unmapped (toMap (KdTree.kNearest tree defaultL key)))))
insertion previous unmappedA unmappedB (UnmappedTerm j _ b) = do
@ -86,7 +93,7 @@ defaultD = 15
defaultL = 2
defaultP = 2
defaultQ = 3
defaultMoveBound = 3
defaultMoveBound = 2
-- | How many nodes to consider for our constant-time approximation to tree edit distance.
defaultM :: Integer