Computes "intelligent" differences between two sequenced Enumerables. This is an implementation of the McIlroy-Hunt "diff" algorithm for Enumerable objects that include Diffable.
Based on Mario I. Wolczko's Smalltalk version (1.2, 1993) and Ned Konz's Perl version (Algorithm::Diff 1.15).
require 'diff/lcs' seq1 = %w(a b c e h j l m n p) seq2 = %w(b c d e f j k l m r s t) lcs = Diff::LCS.lcs(seq1, seq2) diffs = Diff::LCS.diff(seq1, seq2) sdiff = Diff::LCS.sdiff(seq1, seq2) seq = Diff::LCS.traverse_sequences(seq1, seq2, callback_obj) bal = Diff::LCS.traverse_balanced(seq1, seq2, callback_obj) seq2 == Diff::LCS.patch(seq1, diffs) seq2 == Diff::LCS.patch!(seq1, diffs) seq1 == Diff::LCS.unpatch(seq2, diffs) seq1 == Diff::LCS.unpatch!(seq2, diffs) seq2 == Diff::LCS.patch(seq1, sdiff) seq2 == Diff::LCS.patch!(seq1, sdiff) seq1 == Diff::LCS.unpatch(seq2, sdiff) seq1 == Diff::LCS.unpatch!(seq2, sdiff)
Alternatively, objects can be extended with Diff::LCS:
seq1.extend(Diff::LCS) lcs = seq1.lcs(seq2) diffs = seq1.diff(seq2) sdiff = seq1.sdiff(seq2) seq = seq1.traverse_sequences(seq2, callback_obj) bal = seq1.traverse_balanced(seq2, callback_obj) seq2 == seq1.patch(diffs) seq2 == seq1.patch!(diffs) seq1 == seq2.unpatch(diffs) seq1 == seq2.unpatch!(diffs) seq2 == seq1.patch(sdiff) seq2 == seq1.patch!(sdiff) seq1 == seq2.unpatch(sdiff) seq1 == seq2.unpatch!(sdiff)
Default extensions are provided for Array and String objects through the use of 'diff/lcs/array' and 'diff/lcs/string'.
The following text is from the Perl documentation. The only changes have been to make the text appear better in Rdoc.
I once read an article written by the authors of diff; they said that they hard worked very hard on the algorithm until they found the right one.
I think what they ended up using (and I hope someone will correct me, because I am not very confident about this) was the `longest common subsequence' method. In the LCS problem, you have two sequences of items:
a b c d f g h j q z a b c d e f g i j k r x y z
and you want to find the longest sequence of items that is present in both original sequences in the same order. That is, you want to find a new sequence S which can be obtained from the first sequence by deleting some items, and from the second sequence by deleting other items. You also want S to be as long as possible. In this case S is:
a b c d f g j z
From there it's only a small step to get diff-like output:
e h i k q r x y + - + + - + + +
This module solves the LCS problem. It also includes a canned function to generate diff-like output.
It might seem from the example above that the LCS of two sequences is always pretty obvious, but that's not always the case, especially when the two sequences have many repeated elements. For example, consider
a x b y c z p d q a b c a x b y c z
A naive approach might start by matching up the a and b that appear at the beginning of each sequence, like this:
a x b y c z p d q a b c a b y c z
This finds the common subsequence +a b c z+. But actually, the LCS is +a x b y c z+:
a x b y c z p d q a b c a x b y c z
This version is by Austin Ziegler <austin@rubyforge.org>.
It is based on the Perl Algorithm::Diff (1.15) by Ned Konz , copyright © 2000–2002 and the Smalltalk diff version by Mario I. Wolczko, copyright © 1993. Documentation includes work by Mark-Jason Dominus.
Copyright © 2004–2013 Austin Ziegler This program is free software; you can redistribute it and/or modify it under the same terms as Ruby, or alternatively under the Perl Artistic licence.
Much of the documentation is taken directly from the Perl Algorithm::Diff implementation and was written originally by Mark-Jason Dominus and later by Ned Konz. The basic Ruby implementation was re-ported from the Smalltalk implementation, available at st.cs.uiuc.edu/pub/Smalltalk/MANCHESTER/manchester/4.0/diff.st
sdiff and traverse_balanced were written for the Perl version by Mike Schilli <m@perlmeister.com>.
"The algorithm is described in A Fast Algorithm for Computing Longest Common Subsequences, CACM, vol.20, no.5, pp.350-353, May 1977, with a few minor improvements to improve the speed."
An alias for DefaultCallbacks that is used in Diff::LCS#traverse_balanced.
Diff::LCS.LCS(seq1, seq2, Diff::LCS::BalancedCallbacks)
An alias for DefaultCallbacks that is used in Diff::LCS#traverse_sequences.
Diff::LCS.LCS(seq1, seq2, Diff::LCS::SequenceCallbacks)
# File lib/diff/lcs/callbacks.rb, line 48 def self.callbacks_for(callbacks) callbacks.new rescue callbacks end
diff computes the smallest set of additions and deletions necessary to turn the first sequence into the second, and returns a description of these changes.
See Diff::LCS::DiffCallbacks for the default behaviour. An alternate behaviour may be implemented with Diff::LCS::ContextDiffCallbacks. If a Class argument is provided for callbacks, diff will attempt to initialise it. If the callbacks object (possibly initialised) responds to finish, it will be called.
# File lib/diff/lcs.rb, line 244 def diff(seq1, seq2, callbacks = nil, &block) # :yields diff changes: diff_traversal(:diff, seq1, seq2, callbacks || Diff::LCS::DiffCallbacks, &block) end
# File lib/diff/lcs.rb, line 220 def lcs(seq1, seq2, &block) #:yields seq1[i] for each matched: matches = Diff::LCS::Internals.lcs(seq1, seq2) ret = [] string = seq1.kind_of? String matches.each_with_index do |e, i| unless matches[i].nil? v = string ? seq1[i, 1] : seq1[i] v = block[v] if block ret << v end end ret end
Applies a patchset to the sequence src according to the direction (:patch or :unpatch), producing a new sequence.
If the direction is not specified, Diff::LCS::patch will attempt to discover the direction of the patchset.
A patchset can be considered to apply forward (:patch) if the following expression is true:
patch(s1, diff(s1, s2)) -> s2
A patchset can be considered to apply backward (:unpatch) if the following expression is true:
patch(s2, diff(s1, s2)) -> s1
If the patchset contains no changes, the src value will be returned as either src.dup or src. A patchset can be deemed as having no changes if the following predicate returns true:
patchset.empty? or patchset.flatten.all? { |change| change.unchanged? }
A patchset is always an enumerable sequence of changes, hunks of changes, or a mix of the two. A hunk of changes is an enumerable sequence of changes:
[ # patchset # change [ # hunk # change ] ]
The patch method accepts patchsets that are enumerable sequences containing either Diff::LCS::Change objects (or a subclass) or the array representations of those objects. Prior to application, array representations of Diff::LCS::Change objects will be reified.
# File lib/diff/lcs.rb, line 688 def patch(src, patchset, direction = nil) # Normalize the patchset. has_changes, patchset = Diff::LCS::Internals.analyze_patchset(patchset) if not has_changes return src.dup if src.respond_to? :dup return src end string = src.kind_of?(String) # Start with a new empty type of the source's class res = src.class.new direction ||= Diff::LCS::Internals.intuit_diff_direction(src, patchset) ai = bj = 0 patch_map = PATCH_MAP[direction] patchset.flatten.each do |change| # Both Change and ContextChange support #action action = patch_map[change.action] case change when Diff::LCS::ContextChange case direction when :patch el = change.new_element op = change.old_position np = change.new_position when :unpatch el = change.old_element op = change.new_position np = change.old_position end case action when '-' # Remove details from the old string while ai < op res << (string ? src[ai, 1] : src[ai]) ai += 1 bj += 1 end ai += 1 when '+' while bj < np res << (string ? src[ai, 1] : src[ai]) ai += 1 bj += 1 end res << el bj += 1 when '=' # This only appears in sdiff output with the SDiff callback. # Therefore, we only need to worry about dealing with a single # element. res << el ai += 1 bj += 1 when '!' while ai < op res << (string ? src[ai, 1] : src[ai]) ai += 1 bj += 1 end bj += 1 ai += 1 res << el end when Diff::LCS::Change case action when '-' while ai < change.position res << (string ? src[ai, 1] : src[ai]) ai += 1 bj += 1 end ai += 1 when '+' while bj < change.position res << (string ? src[ai, 1] : src[ai]) ai += 1 bj += 1 end bj += 1 res << change.element end end end while ai < src.size res << (string ? src[ai, 1] : src[ai]) ai += 1 bj += 1 end res end
Given a set of patchset, convert the current version to the next version. Does no auto-discovery.
# File lib/diff/lcs.rb, line 801 def patch!(src, patchset) patch(src, patchset, :patch) end
sdiff computes all necessary components to show two sequences and their minimized differences side by side, just like the Unix utility sdiff does:
old < - same same before | after - > new
See Diff::LCS::SDiffCallbacks for the default behaviour. An alternate behaviour may be implemented with Diff::LCS::ContextDiffCallbacks. If a Class argument is provided for callbacks, diff will attempt to initialise it. If the callbacks object (possibly initialised) responds to finish, it will be called.
# File lib/diff/lcs.rb, line 263 def sdiff(seq1, seq2, callbacks = nil, &block) #:yields diff changes: diff_traversal(:sdiff, seq1, seq2, callbacks || Diff::LCS::SDiffCallbacks, &block) end
traverse_balanced is an alternative to traverse_sequences. It uses a different algorithm to iterate through the entries in the computed longest common subsequence. Instead of viewing the changes as insertions or deletions from one of the sequences, traverse_balanced will report changes between the sequences.
The arguments to traverse_balanced are the two sequences to traverse and a callback object, like this:
traverse_balanced(seq1, seq2, Diff::LCS::ContextDiffCallbacks.new)
sdiff is implemented with traverse_balanced.
Optional callback methods are emphasized.
callbacksmatch |
Called when a and b are pointing to common elements in A and B. |
callbacksdiscard_a |
Called when a is pointing to an element not in B. |
callbacksdiscard_b |
Called when b is pointing to an element not in A. |
callbackschange |
Called when a and b are pointing to the same relative position, but A[a] and B[b] are not the same; a change has occurred. |
traverse_balanced might be a bit slower than traverse_sequences, noticable only while processing huge amounts of data.
a---+ v A = a b c e h j l m n p B = b c d e f j k l m r s t ^ b---+
If there are two arrows (a and b) pointing to elements of sequences A and B, the arrows will initially point to the first elements of their respective sequences. traverse_sequences will advance the arrows through the sequences one element at a time, calling a method on the user-specified callback object before each advance. It will advance the arrows in such a way that if there are elements A[i] and B[j] which are both equal and part of the longest common subsequence, there will be some moment during the execution of traverse_sequences when arrow a is pointing to A[i] and arrow b is pointing to B[j]. When this happens, traverse_sequences will call callbacks#match and then it will advance both arrows.
Otherwise, one of the arrows is pointing to an element of its sequence that is not part of the longest common subsequence. traverse_sequences will advance that arrow and will call callbacks#discard_a or callbacks#discard_b, depending on which arrow it advanced.
If both a and b point to elements that are not part of the longest common subsequence, then traverse_sequences will try to call callbacks#change and advance both arrows. If callbacks#change is not implemented, then callbacks#discard_a and callbacks#discard_b will be called in turn.
The methods for callbacks#match, callbacks#discard_a, callbacks#discard_b, and callbacks#change are invoked with an event comprising the action ("=", "+", "-", or "!", respectively), the indicies i and j, and the elements A[i] and B[j]. Return values are discarded by traverse_balanced.
Note that i and j may not be the same index position, even if a and b are considered to be pointing to matching or changed elements.
# File lib/diff/lcs.rb, line 540 def traverse_balanced(seq1, seq2, callbacks = Diff::LCS::BalancedCallbacks) matches = Diff::LCS::Internals.lcs(seq1, seq2) a_size = seq1.size b_size = seq2.size ai = bj = mb = 0 ma = -1 string = seq1.kind_of?(String) # Process all the lines in the match vector. loop do # Find next match indices +ma+ and +mb+ loop do ma += 1 break unless ma < matches.size and matches[ma].nil? end break if ma >= matches.size # end of matches? mb = matches[ma] # Change(seq2) while (ai < ma) or (bj < mb) ax = string ? seq1[ai, 1] : seq1[ai] bx = string ? seq2[bj, 1] : seq2[bj] case [(ai < ma), (bj < mb)] when [true, true] if callbacks.respond_to?(:change) event = Diff::LCS::ContextChange.new('!', ai, ax, bj, bx) event = yield event if block_given? callbacks.change(event) ai += 1 bj += 1 else event = Diff::LCS::ContextChange.new('-', ai, ax, bj, bx) event = yield event if block_given? callbacks.discard_a(event) ai += 1 ax = string ? seq1[ai, 1] : seq1[ai] event = Diff::LCS::ContextChange.new('+', ai, ax, bj, bx) event = yield event if block_given? callbacks.discard_b(event) bj += 1 end when [true, false] event = Diff::LCS::ContextChange.new('-', ai, ax, bj, bx) event = yield event if block_given? callbacks.discard_a(event) ai += 1 when [false, true] event = Diff::LCS::ContextChange.new('+', ai, ax, bj, bx) event = yield event if block_given? callbacks.discard_b(event) bj += 1 end end # Match ax = string ? seq1[ai, 1] : seq1[ai] bx = string ? seq2[bj, 1] : seq2[bj] event = Diff::LCS::ContextChange.new('=', ai, ax, bj, bx) event = yield event if block_given? callbacks.match(event) ai += 1 bj += 1 end while (ai < a_size) or (bj < b_size) ax = string ? seq1[ai, 1] : seq1[ai] bx = string ? seq2[bj, 1] : seq2[bj] case [(ai < a_size), (bj < b_size)] when [true, true] if callbacks.respond_to?(:change) event = Diff::LCS::ContextChange.new('!', ai, ax, bj, bx) event = yield event if block_given? callbacks.change(event) ai += 1 bj += 1 else event = Diff::LCS::ContextChange.new('-', ai, ax, bj, bx) event = yield event if block_given? callbacks.discard_a(event) ai += 1 ax = string ? seq1[ai, 1] : seq1[ai] event = Diff::LCS::ContextChange.new('+', ai, ax, bj, bx) event = yield event if block_given? callbacks.discard_b(event) bj += 1 end when [true, false] event = Diff::LCS::ContextChange.new('-', ai, ax, bj, bx) event = yield event if block_given? callbacks.discard_a(event) ai += 1 when [false, true] event = Diff::LCS::ContextChange.new('+', ai, ax, bj, bx) event = yield event if block_given? callbacks.discard_b(event) bj += 1 end end end
traverse_sequences is the most general facility provided by this module; diff and lcs are implemented as calls to it.
The arguments to traverse_sequences are the two sequences to traverse, and a callback object, like this:
traverse_sequences(seq1, seq2, Diff::LCS::ContextDiffCallbacks.new)
Optional callback methods are emphasized.
callbacksmatch |
Called when a and b are pointing to common elements in A and B. |
callbacksdiscard_a |
Called when a is pointing to an element not in B. |
callbacksdiscard_b |
Called when b is pointing to an element not in A. |
callbacksfinished_a |
Called when a has reached the end of sequence A. |
callbacksfinished_b |
Called when b has reached the end of sequence B. |
a---+ v A = a b c e h j l m n p B = b c d e f j k l m r s t ^ b---+
If there are two arrows (a and b) pointing to elements of sequences A and B, the arrows will initially point to the first elements of their respective sequences. traverse_sequences will advance the arrows through the sequences one element at a time, calling a method on the user-specified callback object before each advance. It will advance the arrows in such a way that if there are elements A[i] and B[j] which are both equal and part of the longest common subsequence, there will be some moment during the execution of traverse_sequences when arrow a is pointing to A[i] and arrow b is pointing to B[j]. When this happens, traverse_sequences will call callbacks#match and then it will advance both arrows.
Otherwise, one of the arrows is pointing to an element of its sequence that is not part of the longest common subsequence. traverse_sequences will advance that arrow and will call callbacks#discard_a or callbacks#discard_b, depending on which arrow it advanced. If both arrows point to elements that are not part of the longest common subsequence, then traverse_sequences will advance one of them and call the appropriate callback, but it is not specified which it will call.
The methods for callbacks#match, callbacks#discard_a, and callbacks#discard_b are invoked with an event comprising the action ("=", "+", or "-", respectively), the indicies i and j, and the elements A[i] and B[j]. Return values are discarded by traverse_sequences.
If arrow a reaches the end of its sequence before arrow b does, traverse_sequence will try to call callbacks#finished_a with the last index and element of A (A[-1]) and the current index and element of B (B[j]). If callbacks#finished_a does not exist, then callbacks#discard_b will be called on each element of B until the end of the sequence is reached (the call will be done with A[-1] and B[j] for each element).
If b reaches the end of B before a reaches the end of A, callbacks#finished_b will be called with the current index and element of A (A[i]) and the last index and element of B (A[-1]). Again, if callbacks#finished_b does not exist on the callback object, then callbacks#discard_a will be called on each element of A until the end of the sequence is reached (A[i] and B[-1]).
There is a chance that one additional callbacks#discard_a or callbacks#discard_b will be called after the end of the sequence is reached, if a has not yet reached the end of A or b has not yet reached the end of B.
# File lib/diff/lcs.rb, line 349 def traverse_sequences(seq1, seq2, callbacks = Diff::LCS::SequenceCallbacks, &block) #:yields change events: callbacks ||= Diff::LCS::SequenceCallbacks matches = Diff::LCS::Internals.lcs(seq1, seq2) run_finished_a = run_finished_b = false string = seq1.kind_of?(String) a_size = seq1.size b_size = seq2.size ai = bj = 0 (0..matches.size).each do |i| b_line = matches[i] ax = string ? seq1[i, 1] : seq1[i] bx = string ? seq2[bj, 1] : seq2[bj] if b_line.nil? unless ax.nil? or (string and ax.empty?) event = Diff::LCS::ContextChange.new('-', i, ax, bj, bx) event = yield event if block_given? callbacks.discard_a(event) end else loop do break unless bj < b_line bx = string ? seq2[bj, 1] : seq2[bj] event = Diff::LCS::ContextChange.new('+', i, ax, bj, bx) event = yield event if block_given? callbacks.discard_b(event) bj += 1 end bx = string ? seq2[bj, 1] : seq2[bj] event = Diff::LCS::ContextChange.new('=', i, ax, bj, bx) event = yield event if block_given? callbacks.match(event) bj += 1 end ai = i end ai += 1 # The last entry (if any) processed was a match. +ai+ and +bj+ point # just past the last matching lines in their sequences. while (ai < a_size) or (bj < b_size) # last A? if ai == a_size and bj < b_size if callbacks.respond_to?(:finished_a) and not run_finished_a ax = string ? seq1[-1, 1] : seq1[-1] bx = string ? seq2[bj, 1] : seq2[bj] event = Diff::LCS::ContextChange.new('>', (a_size - 1), ax, bj, bx) event = yield event if block_given? callbacks.finished_a(event) run_finished_a = true else ax = string ? seq1[ai, 1] : seq1[ai] loop do bx = string ? seq2[bj, 1] : seq2[bj] event = Diff::LCS::ContextChange.new('+', ai, ax, bj, bx) event = yield event if block_given? callbacks.discard_b(event) bj += 1 break unless bj < b_size end end end # last B? if bj == b_size and ai < a_size if callbacks.respond_to?(:finished_b) and not run_finished_b ax = string ? seq1[ai, 1] : seq1[ai] bx = string ? seq2[-1, 1] : seq2[-1] event = Diff::LCS::ContextChange.new('<', ai, ax, (b_size - 1), bx) event = yield event if block_given? callbacks.finished_b(event) run_finished_b = true else bx = string ? seq2[bj, 1] : seq2[bj] loop do ax = string ? seq1[ai, 1] : seq1[ai] event = Diff::LCS::ContextChange.new('-', ai, ax, bj, bx) event = yield event if block_given? callbacks.discard_a(event) ai += 1 break unless bj < b_size end end end if ai < a_size ax = string ? seq1[ai, 1] : seq1[ai] bx = string ? seq2[bj, 1] : seq2[bj] event = Diff::LCS::ContextChange.new('-', ai, ax, bj, bx) event = yield event if block_given? callbacks.discard_a(event) ai += 1 end if bj < b_size ax = string ? seq1[ai, 1] : seq1[ai] bx = string ? seq2[bj, 1] : seq2[bj] event = Diff::LCS::ContextChange.new('+', ai, ax, bj, bx) event = yield event if block_given? callbacks.discard_b(event) bj += 1 end end end
Returns the difference set between self and other. See Diff::LCS#diff.
# File lib/diff/lcs.rb, line 148 def diff(other, callbacks = nil, &block) Diff::LCS.diff(self, other, callbacks, &block) end
Attempts to patch self with the provided patchset. A new sequence based on self and the patchset will be created. See Diff::LCS#patch. Attempts to autodiscover the direction of the patch.
# File lib/diff/lcs.rb, line 176 def patch(patchset) Diff::LCS.patch(self, patchset) end
Attempts to patch self with the provided patchset. A new sequence based on self and the patchset will be created. See Diff::LCS#patch. Does no patch direction autodiscovery.
# File lib/diff/lcs.rb, line 184 def patch!(patchset) Diff::LCS.patch!(self, patchset) end
Attempts to patch self with the provided patchset, using patch!. If the sequence this is used on supports replace, the value of self will be replaced. See Diff::LCS#patch. Does no patch direction autodiscovery.
# File lib/diff/lcs.rb, line 198 def patch_me(patchset) if respond_to? :replace replace(patch!(patchset)) else patch!(patchset) end end
Returns the balanced ("side-by-side") difference set between self and other. See Diff::LCS#sdiff.
# File lib/diff/lcs.rb, line 154 def sdiff(other, callbacks = nil, &block) Diff::LCS.sdiff(self, other, callbacks, &block) end
Traverses the discovered longest common subsequences between self and other using the alternate, balanced algorithm. See Diff::LCS#traverse_balanced.
# File lib/diff/lcs.rb, line 168 def traverse_balanced(other, callbacks = nil, &block) traverse_balanced(self, other, callbacks || Diff::LCS.YieldingCallbacks, &block) end
Traverses the discovered longest common subsequences between self and other. See Diff::LCS#traverse_sequences.
# File lib/diff/lcs.rb, line 160 def traverse_sequences(other, callbacks = nil, &block) traverse_sequences(self, other, callbacks || Diff::LCS.YieldingCallbacks, &block) end
Attempts to unpatch self with the provided patchset. A new sequence based on self and the patchset will be created. See Diff::LCS#unpatch. Does no patch direction autodiscovery.
# File lib/diff/lcs.rb, line 191 def unpatch!(patchset) Diff::LCS.unpatch!(self, patchset) end
Attempts to unpatch self with the provided patchset, using unpatch!. If the sequence this is used on supports replace, the value of self will be replaced. See Diff::LCS#unpatch. Does no patch direction autodiscovery.
# File lib/diff/lcs.rb, line 210 def unpatch_me(patchset) if respond_to? :replace replace(unpatch!(patchset)) else unpatch!(patchset) end end
Generated with the Darkfish Rdoc Generator 2.