Function trigramDistance() added for string similarity search #4466
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danlark1
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For changelog. Remove if this is non-significant change.
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Short description (up to few sentences):
Trigram distance was added. It is similar to q-gram metrics in R language. I call it trigramDistance()
Detailed description (optional):
OLD:We compute all the trigrams from needle and haystack, calculate the symmetric difference between these two sets and normalize by dividing to the sum of lengths. The speed is not that great but this metric is known to be one of the fastest.
NEW:
Distance function implementation.
We calculate all the trigrams from left string and count by the index of 16 bits hash of them in the map.
Then calculate all the trigrams from the right string and calculate the trigram distance on the flight by adding and subtracting from the hashmap. Then return the map into the condition of which it was after the left string calculation. If the right string size is big (more than 2**15 bytes), the strings are not similar at all and we return 1.