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lib/Algorithm/Diff.pm  view on Meta::CPAN

                # oddly, it's faster to always test this (CPU cache?).
                if ( defined($k) )
                {
                    $links->[$k] =
                      [ ( $k ? $links->[ $k - 1 ] : undef ), $i, $j ];
                }
            }
        }
    }

    if (@$thresh)
    {
        return $prunedCount + @$thresh if $counting;
        for ( my $link = $links->[$#$thresh] ; $link ; $link = $link->[0] )
        {
            $matchVector->[ $link->[1] ] = $link->[2];
        }
    }
    elsif ($counting)
    {
        return $prunedCount;
    }

    return wantarray ? @$matchVector : $matchVector;
}

sub traverse_sequences
{
    my $a                 = shift;          # array ref
    my $b                 = shift;          # array ref
    my $callbacks         = shift || {};
    my $keyGen            = shift;
    my $matchCallback     = $callbacks->{'MATCH'} || sub { };
    my $discardACallback  = $callbacks->{'DISCARD_A'} || sub { };
    my $finishedACallback = $callbacks->{'A_FINISHED'};
    my $discardBCallback  = $callbacks->{'DISCARD_B'} || sub { };
    my $finishedBCallback = $callbacks->{'B_FINISHED'};
    my $matchVector = _longestCommonSubsequence( $a, $b, 0, $keyGen, @_ );

    # Process all the lines in @$matchVector
    my $lastA = $#$a;
    my $lastB = $#$b;
    my $bi    = 0;
    my $ai;

    for ( $ai = 0 ; $ai <= $#$matchVector ; $ai++ )
    {
        my $bLine = $matchVector->[$ai];
        if ( defined($bLine) )    # matched
        {
            &$discardBCallback( $ai, $bi++, @_ ) while $bi < $bLine;
            &$matchCallback( $ai,    $bi++, @_ );
        }
        else
        {
            &$discardACallback( $ai, $bi, @_ );
        }
    }

    # The last entry (if any) processed was a match.
    # $ai and $bi point just past the last matching lines in their sequences.

    while ( $ai <= $lastA or $bi <= $lastB )
    {

        # last A?
        if ( $ai == $lastA + 1 and $bi <= $lastB )
        {
            if ( defined($finishedACallback) )
            {
                &$finishedACallback( $lastA, @_ );
                $finishedACallback = undef;
            }
            else
            {
                &$discardBCallback( $ai, $bi++, @_ ) while $bi <= $lastB;
            }
        }

        # last B?
        if ( $bi == $lastB + 1 and $ai <= $lastA )
        {
            if ( defined($finishedBCallback) )
            {
                &$finishedBCallback( $lastB, @_ );
                $finishedBCallback = undef;
            }
            else
            {
                &$discardACallback( $ai++, $bi, @_ ) while $ai <= $lastA;
            }
        }

        &$discardACallback( $ai++, $bi, @_ ) if $ai <= $lastA;
        &$discardBCallback( $ai, $bi++, @_ ) if $bi <= $lastB;
    }

    return 1;
}

sub traverse_balanced
{
    my $a                 = shift;              # array ref
    my $b                 = shift;              # array ref
    my $callbacks         = shift || {};
    my $keyGen            = shift;
    my $matchCallback     = $callbacks->{'MATCH'} || sub { };
    my $discardACallback  = $callbacks->{'DISCARD_A'} || sub { };
    my $discardBCallback  = $callbacks->{'DISCARD_B'} || sub { };
    my $changeCallback    = $callbacks->{'CHANGE'};
    my $matchVector = _longestCommonSubsequence( $a, $b, 0, $keyGen, @_ );

    # Process all the lines in match vector
    my $lastA = $#$a;
    my $lastB = $#$b;
    my $bi    = 0;
    my $ai    = 0;
    my $ma    = -1;
    my $mb;

lib/Algorithm/Diff.pm  view on Meta::CPAN

Note that the hunks will always alternate between those that are part of
the LCS (those that contain unchanged items) and those that contain
changes.  This means that all we need to be told is whether the first
hunk is a 'same' or 'diff' hunk and we can determine which of the other
hunks contain 'same' items or 'diff' items.

By convention, we always make the first hunk contain unchanged items.
So the 1st, 3rd, 5th, etc. hunks (all odd-numbered hunks if you start
counting from 1) all contain unchanged items.  And the 2nd, 4th, 6th,
etc. hunks (all even-numbered hunks if you start counting from 1) all
contain changed items.

Since @a and @b don't begin with the same value, the first hunk in our
example is empty (otherwise we'd violate the above convention).  Note
that the first 4 index values in our example are all zero.  Plug these
values into our previous code block and we get:

    @hunk1a = @a[ 0 .. 0-1 ];
    @hunk1b = @b[ 0 .. 0-1 ];

And C<0..-1> returns the empty list.

Move down one pair of indices (2..5) and we get the offset ranges for
the second hunk, which contains changed items.

Since C<@diff[2..5]> contains (0,0,1,0) in our example, the second hunk
consists of these two lists of items:

        @hunk2a = @a[ $cdiff[2] .. $cdiff[4]-1 ];
        @hunk2b = @b[ $cdiff[3] .. $cdiff[5]-1 ];
    # or
        @hunk2a = @a[ 0 .. 1-1 ];
        @hunk2b = @b[ 0 .. 0-1 ];
    # or
        @hunk2a = @a[ 0 .. 0 ];
        @hunk2b = @b[ 0 .. -1 ];
    # or
        @hunk2a = ( 'a' );
        @hunk2b = ( );

That is, we would delete item 0 ('a') from @a.

Since C<@diff[4..7]> contains (1,0,3,2) in our example, the third hunk
consists of these two lists of items:

        @hunk3a = @a[ $cdiff[4] .. $cdiff[6]-1 ];
        @hunk3a = @b[ $cdiff[5] .. $cdiff[7]-1 ];
    # or
        @hunk3a = @a[ 1 .. 3-1 ];
        @hunk3a = @b[ 0 .. 2-1 ];
    # or
        @hunk3a = @a[ 1 .. 2 ];
        @hunk3a = @b[ 0 .. 1 ];
    # or
        @hunk3a = qw( b c );
        @hunk3a = qw( b c );

Note that this third hunk contains unchanged items as our convention demands.

You can continue this process until you reach the last two indices,
which will always be the number of items in each sequence.  This is
required so that subtracting one from each will give you the indices to
the last items in each sequence.

=head2 C<traverse_sequences>

C<traverse_sequences> used to be the most general facility provided by
this module (the new OO interface is more powerful and much easier to
use).

Imagine that there are two arrows.  Arrow A points to an element of
sequence A, and arrow B points to an element of the sequence B. 
Initially, the arrows point to the first elements of the respective
sequences.  C<traverse_sequences> will advance the arrows through the
sequences one element at a time, calling an appropriate user-specified
callback function before each advance.  It will advance the arrows in
such a way that if there are equal elements C<$A[$i]> and C<$B[$j]>
which are equal and which are part of the LCS, there will be some moment
during the execution of C<traverse_sequences> when arrow A is pointing
to C<$A[$i]> and arrow B is pointing to C<$B[$j]>.  When this happens,
C<traverse_sequences> will call the C<MATCH> callback function 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 LCS.  C<traverse_sequences> will advance that
arrow and will call the C<DISCARD_A> or the C<DISCARD_B> callback,
depending on which arrow it advanced.  If both arrows point to elements
that are not part of the LCS, then C<traverse_sequences> will advance
one of them and call the appropriate callback, but it is not specified
which it will call.

The arguments to C<traverse_sequences> are the two sequences to
traverse, and a hash which specifies the callback functions, like this:

    traverse_sequences(
        \@seq1, \@seq2,
        {   MATCH => $callback_1,
            DISCARD_A => $callback_2,
            DISCARD_B => $callback_3,
        }
    );

Callbacks for MATCH, DISCARD_A, and DISCARD_B are invoked with at least
the indices of the two arrows as their arguments.  They are not expected
to return any values.  If a callback is omitted from the table, it is
not called.

Callbacks for A_FINISHED and B_FINISHED are invoked with at least the
corresponding index in A or B.

If arrow A reaches the end of its sequence, before arrow B does,
C<traverse_sequences> will call the C<A_FINISHED> callback when it
advances arrow B, if there is such a function; if not it will call
C<DISCARD_B> instead.  Similarly if arrow B finishes first. 
C<traverse_sequences> returns when both arrows are at the ends of their
respective sequences.  It returns true on success and false on failure. 
At present there is no way to fail.

C<traverse_sequences> may be passed an optional fourth parameter; this
is a CODE reference to a key generation function.  See L</KEY GENERATION
FUNCTIONS>.

Additional parameters, if any, will be passed to the key generation function.

If you want to pass additional parameters to your callbacks, but don't
need a custom key generation function, you can get the default by
passing undef:

    traverse_sequences(
        \@seq1, \@seq2,
        {   MATCH => $callback_1,
            DISCARD_A => $callback_2,
            DISCARD_B => $callback_3,
        },
        undef,     # default key-gen
        $myArgument1,
        $myArgument2,
        $myArgument3,
    );

C<traverse_sequences> does not have a useful return value; you are
expected to plug in the appropriate behavior with the callback
functions.

=head2 C<traverse_balanced>

C<traverse_balanced> is an alternative to C<traverse_sequences>. It
uses a different algorithm to iterate through the entries in the
computed LCS. Instead of sticking to one side and showing element changes
as insertions and deletions only, it will jump back and forth between
the two sequences and report I<changes> occurring as deletions on one
side followed immediately by an insertion on the other side.

In addition to the C<DISCARD_A>, C<DISCARD_B>, and C<MATCH> callbacks
supported by C<traverse_sequences>, C<traverse_balanced> supports
a C<CHANGE> callback indicating that one element got C<replaced> by another:

    traverse_balanced(
        \@seq1, \@seq2,
        {   MATCH => $callback_1,
            DISCARD_A => $callback_2,
            DISCARD_B => $callback_3,
            CHANGE    => $callback_4,
        }
    );

If no C<CHANGE> callback is specified, C<traverse_balanced>
will map C<CHANGE> events to C<DISCARD_A> and C<DISCARD_B> actions,
therefore resulting in a similar behaviour as C<traverse_sequences>
with different order of events.

C<traverse_balanced> might be a bit slower than C<traverse_sequences>,
noticeable only while processing huge amounts of data.

The C<sdiff> function of this module 
is implemented as call to C<traverse_balanced>.

C<traverse_balanced> does not have a useful return value; you are expected to
plug in the appropriate behavior with the callback functions.

=head1 KEY GENERATION FUNCTIONS

Most of the functions accept an optional extra parameter.  This is a
CODE reference to a key generating (hashing) function that should return
a string that uniquely identifies a given element.  It should be the
case that if two elements are to be considered equal, their keys should
be the same (and the other way around).  If no key generation function
is provided, the key will be the element as a string.

By default, comparisons will use "eq" and elements will be turned into keys
using the default stringizing operator '""'.

Where this is important is when you're comparing something other than
strings.  If it is the case that you have multiple different objects
that should be considered to be equal, you should supply a key
generation function. Otherwise, you have to make sure that your arrays
contain unique references.

For instance, consider this example:

    package Person;

    sub new
    {
        my $package = shift;
        return bless { name => '', ssn => '', @_ }, $package;
    }

    sub clone
    {
        my $old = shift;
        my $new = bless { %$old }, ref($old);
    }

    sub hash
    {
        return shift()->{'ssn'};
    }

    my $person1 = Person->new( name => 'Joe', ssn => '123-45-6789' );
    my $person2 = Person->new( name => 'Mary', ssn => '123-47-0000' );
    my $person3 = Person->new( name => 'Pete', ssn => '999-45-2222' );
    my $person4 = Person->new( name => 'Peggy', ssn => '123-45-9999' );
    my $person5 = Person->new( name => 'Frank', ssn => '000-45-9999' );

If you did this:

    my $array1 = [ $person1, $person2, $person4 ];
    my $array2 = [ $person1, $person3, $person4, $person5 ];
    Algorithm::Diff::diff( $array1, $array2 );

everything would work out OK (each of the objects would be converted
into a string like "Person=HASH(0x82425b0)" for comparison).