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POFast fuzzy/approximate search in dictionary of strings in Ruby
 

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  1. POFast fuzzy/approximate search in dictionary of strings in Ruby
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    <p>I have a dictionary of 50K to 100K strings (can be up to 50+ characters) and I am trying to find whether a given string is in the dictionary with some "edit" distance tolerance. (Levenshtein for example). I am fine pre-computing any type of data structure before doing the search.</p> <p><strong>My goal to run thousands of strings against that dictionary as fast as possible and returns the closest neighbor. I would be fine just getting a boolean that say whether a given is in the dictionary or not if there was a significantly faster algorithm to do so</strong></p> <p>For this, I first tried to compute all the Levenshtein distances and take the minimum and it was obviously horribly slow. So I tried to implement a Levenshtein Trie based on this article <a href="http://stevehanov.ca/blog/index.php?id=114">http://stevehanov.ca/blog/index.php?id=114</a></p> <p>See my gist here for reproducing the benchmark: <a href="https://gist.github.com/nicolasmeunier/7493947">https://gist.github.com/nicolasmeunier/7493947</a></p> <p>Here are a few benchmarks I got on my machine:</p> <p><strong>Edit distance of 0 (perfect match)</strong></p> <pre><code>Benchmark.measure { 10.times { dictionary.search(random_word, 0) } } &lt;Benchmark::Tms:0x007fa59bad8908 @label="", @real=0.010889, @cstime=0.0, @cutime=0.0, @stime=0.0, @utime=0.00999999999999801, @total=0.00999999999999801&gt; </code></pre> <p>*<em>Edit distance of 2, it becomes a LOT slower *</em></p> <pre><code>Benchmark.measure { 10.times { dictionary.search(random_word, 2) } } &lt;Benchmark::Tms:0x007fa58c9ca778 @label="", @real=3.404604, @cstime=0.0, @cutime=0.0, @stime=0.020000000000000018, @utime=3.3900000000000006, @total=3.4100000000000006&gt; </code></pre> <p>And it goes downhill from there and become extremely slow for edit distance larger than 2. (1+ second on average per tested string).</p> <p>I would like to know how/if I could speed this up significantly. If there are existing solutions already implemented in ruby/gems, I also don't want to reinvent the wheel...</p> <p>EDIT 1: In my case, I expect most of the strings I am matching against the dictionary NOT to be in there. So if there are any algorithm to quickly discard a string, that could really help.</p> <p>Thanks, Nicolas</p>
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    1. CONicolas, I'm hesitant to comment because I'm not familiar with the literature and don't want to sidetrack the discussion, but I was reminded of a problem I had many moons ago, that of determining if a file was identical to any file in a large "library" on a remote computer. I indexed the files on a "file signature", the signature being the result of a type of CRC (cyclic redundancy check) calculation (a Fixnum, but I don't recall how many bytes). It was very fast and 100% accurate. The idea would be to calculate a signature for each string and then look that up in the index.
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      1. USCary Swoveland
    2. COWere you looking for 100% identical files or did that allow for any margin of error? Was that something you could control? I will look into it more. Thanks for the suggestion.
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    3. CODid you try [this](https://github.com/kiyoka/fuzzy-string-match) and [this](https://github.com/seamusabshere/fuzzy_match)?
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