Re: Need help comparing lines in two files

[drieux]

On Jan 22, 2004, at 4:52 PM, [EMAIL PROTECTED] wrote:

This very green newbie would like to compare two files, let's say File1
and File2.   I
want to put the difference from File2 only, into a new file, File3.
For example:

File1.txt
oranges
apples
bananas
File2.txt
apples
kiwi
bananas
The result I want for File3 is the new entry in File2, which is kiwi.  
(I
don't care that oranges was in File1 and not File2.)
in theory then file2.txt could have been

        oranges
        apples
        kiwi
        banana
what about
        apples
        kiwi
        wombat
        bananas
you would want to have kiwi and wombat

One strategy would be say:
        my @file1 = qw(oranges apples bananas);
        my @file2 = qw(apples kiwi bananas frodo bagins);
        
        my @list = get_diff_list([EMAIL PROTECTED],[EMAIL PROTECTED]);
        
        print "we see $_\n" foreach(@list);
        
        #------------------------
        #
        sub get_diff_list
        {
                my ($list1, $list2 ) = @_;
                
                my %hash = map { $_ => 1 } @$list1;
                
                my @ret_list;
                foreach (@$list2)
                {
                        if ( $hash{$_} )
                        {
                                delete( $hash{$_} );
                        } else {
                                push(@ret_list,$_);
                        }
                }
                # if you wanted to have the remaining bits that were
                # in list1 and not in list2
                #push(@ret_list,$_) foreach(keys(%hash));
                @ret_list;
                
        } # end of get_diff_list
or how about

        sub get_diff_list
        {
                my ($list1, $list2 ) = @_;
                
                my %hash = map { $_ => 1 } @$list1;
                grep { $_ if ( ! exists($hash{$_})) } @$list2;
        }
ciao
drieux
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