Approximate Regular Expression Matching for Java. prex determines the matching distance between a string s and a regular expression r, i.e. how many insertions, deletions and substitutions on s are at least required (minimum cost) such that the resulting string s' is acceptable by r.
The prex algorithm is inspired by the work of Myers and Millers who provide an algorithm for solving the approximate regular expression matching problem. However, their approach requires a special pre-computed data-structure called edit-graph e that encodes all possible matches and mismatches of s with respect to r which requires approximately 15xSxR edges and SxR vertices where S denotes the length of s and R is the length of r. Given that data structure, their approach searches a minimal cost path in e with a worst-case time complexity of O(SxR). The main strengths of Myers and Millers approach are the possibility to use real-valued costs for insertion, deletion and substitution, respectively, and its worst-case time complexity. The drawback, however, is that the edit-graph has to be created upfront.
Similar to Myers and Millers approach, one can also define real-valued cost for deletion, insertion and substitution in prex. However, prex is based on the branch and bounds method (+ extended list) and does not rely on a precomputed edit-graph. Because, prex is using branch and bounds, in theory it has the same worst-case time complexity as exhaustive search. However, our goal is to keep the algorithm as simple as possible and to achieve a reasonable performance in practice by incorporating heuristics.
prex can be used as a standalone command line tool or as a library.
One could compile prex by running mvn package on the command line. The resulting jar archive
can be called with java -jar prex.jar and provides the following command line options:
| Option | Description |
|---|---|
| -c,--cost <cost> | cost values <insertion> <substitution> <deletion> |
| -h | print this message |
| -ic,--ignore-case | ignore case of s when matching against r |
| -n,--normalize | normalize cost to a value in range [0,1] |
| -r,--regex <regex> | regular expression |
| -s,--string <string> | constant string |
| -t,--print-tree | print branch and bounds edit tree |
Please note that the regex syntax is based on dk.brics and that paramters passed to prex should be quoted to prevent globbing. In case you need quotes with inside your string or you regex pattern, you could escape them as illustrated in the example below.
java -jar prex.jar -c 1.0 1.0 1.0 -s "\"" -r "\\\""
input-string: '"'
input-regex: '\"'
Cost : 0.0
The pattern \" for the s parameter is equivalent to the quote character since it is treated as a normal Java string. The parameter passed through the r paramter is interpreted differently, because the regular expression syntax is based on dk.brics; the pattern \\\" is interpreted as a quote charater.
The following code snippet shows how to use prex after the jar file
is imported into your project:
// invoke Prex constructor with regular expression definition,
// r = gcg[abc]+
// default costs for substitution, insertion and deletion are 1.0,
// but they are modifiable
Prex am = new Prex("gcg[abc]+");
// get cost to make s = GCGa matching r = gcg[abc]+
// ignore case and return a value in range [0,1]
System.out.println(am.evaluateCost("GCGa", true, true));
// get cost to make s = GCGa matching r = gcg[abc]+
// do not ignore case and return a value in range [0,1]
System.out.println("GCGa", false, true));
// ignore case and do not normalize
System.out.println(am.evaluateCost("GCGa", true, false));
// do not ignore case and do not normalize
System.out.println(am.evaluateCost("GCGa", false, false));The results of the invocations above look as follows:
0.0
0.75
0.0
3.0Please have a look at the test cases and constructors provided by the
Prex Java class to get additional information about the usage of prex.
The MIT License (MIT)
Copyright (c) 2016 Julian Thome julian.thome.de@gmail.com
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