String Searching Algorithms

8.12

String Searching Algorithms🔗ℹ

Shawn Wagner <shawnw.mobile@gmail.com>

1 Searching for single strings

2 Searching for multiple strings

(require string-searchers)

package: string-searchers

Provides a variety of string search algorithms written in Typed Racket. They look for sequences of exact code points or bytes, not equivalencies. When using with non-ASCII text, consider normalizing strings first.

1 Searching for single strings🔗ℹ

Functions for searching for a single substring in strings.

1.1 Knuth-Morris-Pratt🔗ℹ

Search for strings using the Knuth-Morris-Pratt algorithm. These functions are also available in the string-searchers/kmp module, without the kmp- prefix.

procedure
(kmp-string-contains haystack
needle
[ start
end]) → (Option Index)
  haystack : String
  needle : String
  start : Index = 0
  end : Index = (string-length haystack)

Returns the first index of haystack where needle occurs, or #f if not found. If searching for the same substring many times, prefer compiling a matcher object and using the following functions instead.

procedure
(kmp-string-contains-ci haystack
needle
[ start
end]) → (Option Index)
  haystack : String
  needle : String
  start : Index = 0
  end : Index = (string-length haystack)

Returns the first index of haystack where needle occurs, ignoring case, or #f if not found. If searching for the same substring many times, prefer compiling a matcher object and using the following functions instead.

procedure
(kmp-make-matcher pattern
[ #:case-insensitive case-insensitive?])
→ kmp-matcher
pattern : String
case-insensitive? : Boolean = #f

Compiles a search string into a matcher object, optionally using case-insensitive searching.

procedure
(kmp-matcher? obj) → Boolean
obj : Any

Returns true if its argument is a kmp-matcher object.

procedure
(kmp-matcher-ci? m) → Boolean
m : kmp-matcher

Tests if a matcher is case-insensitive or not

procedure
(kmp-matcher-pattern m) → String
m : kmp-matcher

Returns the search string for this matcher.

procedure
(kmp-find-string m text [start end]) → (Option Index)
  m : kmp-matcher
  text : String
  start : Index = 0
  end : Index = (string-length text)

Return the index of the first occurance of the matcher’s search string in text, or #f if not found.

procedure
(kmp-find-all-strings m
text
[ start
end
#:overlap overlap?]) → (Listof Index)
  m : kmp-matcher
  text : String
  start : Index = 0
  end : Index = (string-length text)
  overlap? : Boolean = #t

Return the indexs of all occurances of the matcher’s search string in text, or an empty list if not found. If the overlap option is true, found matches can overlap - searching for "bb" in "bbb" will return '(0 1) when true, (0) when false.

1.2 Boyer-Moore-Horspool🔗ℹ

Search for strings using the Boyer-Moore-Horspool algorithm. These functions are also available in the string-searchers/bmh module, without the bmh- prefix.

1.2.1 Strings🔗ℹ

procedure
(bmh-string-contains haystack
needle
[ start
end]) → (Option Index)
  haystack : String
  needle : String
  start : Index = 0
  end : Index = (string-length haystack)

procedure
(bmh-string-contains-ci haystack
needle
[ start
end]) → (Option Index)
  haystack : String
  needle : String
  start : Index = 0
  end : Index = (string-length haystack)

procedure
(bmh-make-matcher pattern
[ #:case-insensitive case-insensitive?])
→ bmh-matcher
pattern : String
case-insensitive? : Boolean = #f

Compiles a search string into a matcher object, optionally using case-insensitive searching.

procedure
(bmh-matcher? obj) → Boolean
obj : Any

Returns true if its argument is a bmh-matcher object.

procedure
(bmh-matcher-ci? m) → Boolean
m : bmh-matcher

Tests if a matcher is case-insensitive or not

procedure
(bmh-matcher-pattern m) → String
m : bmh-matcher

Returns the search string for this matcher.

procedure
(bmh-find-string m text [start end]) → (Option Index)
  m : bmh-matcher
  text : String
  start : Index = 0
  end : Index = (string-length text)

Return the index of the first occurance of the matcher’s search string in text, or #f if not found.

procedure
(bmh-find-all-strings m
text
[ start
end
#:overlap overlap?]) → (Listof Index)
  m : bmh-matcher
  text : String
  start : Index = 0
  end : Index = (string-length text)
  overlap? : Boolean = #t

Return the indexes of all occurances of the matcher’s search string in text, or an empty list if not found. If the overlap option is true, found matches can overlap - searching for "bb" in "bbb" will return '(0 1) when true, '(0) when false.

1.2.2 Byte Strings🔗ℹ

Note: There are no case-insensitive routines for byte strings.

procedure
(bmh-byte-string-contains haystack
needle
[ start
end]) → (Option Index)
  haystack : Bytes
  needle : Bytes
  start : Index = 0
  end : Index = (bytes-length haystack)

procedure
(bmh-make-byte-matcher pattern) → bmh-byte-matcher
pattern : Bytes

Return a new matcher that searches for the given byte string.

procedure
(bmh-byte-matcher? obj) → Boolean
obj : Any

Returns true if its argument is a bmh-byte-matcher object.

procedure
(bmh-byte-matcher-pattern m) → Bytes
m : bmh-byte-matcher

Returns the search byte string for this matcher.

procedure
(bmh-find-byte-string m text [start end]) → (Option Index)
  m : bmh-byte-matcher
  text : Bytes
  start : Index = 0
  end : Index = (bytes-length text)

Return the index of the first occurance of the matcher’s search byte string in text, or #f if not found.

procedure
(bmh-find-all-byte-strings m
text
[ start
end
#:overlap overlap?]) → (Listof Index)
  m : bmh-byte-matcher
  text : Bytes
  start : Index = 0
  end : Index = (bytes-length text)
  overlap? : Boolean = #t

Return the indexes of all occurances of the matcher’s search byte string in text, or an empty list if not found. If the overlap option is true, found matches can overlap - searching for #"bb" in #"bbb" will return '(0 1) when true, '(0) when false.

2 Searching for multiple strings🔗ℹ

Sections for searching for any of multiple different substrings in a string.

2.1 Aho-Corasick🔗ℹ

Search for strings using the Aho-Corasick algorithm. These functions are also available in the string-searchers/ahoc module, without the ahoc- prefix.

procedure
(ahoc-make-matcher s ...) → ahoc-matcher
s : String

Create a new Aho-Corasick matcher object that looks for the given string(s).

procedure
(list->ahoc-matcher strings) → ahoc-matcher
strings : (Listof String)

Create a new Aho-Corasick matcher object that looks for the string(s) in the given list.

procedure
(ahoc-matcher? obj) → Boolean
obj : Any

Tests if its argument is an Aho-Corasick matcher or not.

procedure
(ahoc-matcher-patterns m) → (Listof String)
m : ahoc-matcher

Return the search strings this matcher looks for.

procedure
(ahoc-find-string m text) → (Option (Pair Index String))
m : ahoc-matcher
text : String

Returns the first index of a matched string and which string it is, or #f if there are no matches.

procedure
(ahoc-find-allstrings m text) → (List (Pair Index String))
m : ahoc-matcher
text : String

Returns the locations of all matched strings, or an empty list if none match. If one of the search strings is a prefix of another, multiple results can have the same index.

1	Searching for single strings
2	Searching for multiple strings