Perl Array of regular expressions -- matching elements of an array

Question

I am trying to match and remove elements from an array called @array. The elements to be removed must match the patterns stored inside an array called @del_pattern

my @del_pattern = ('input', 'output', 'wire', 'reg', '\b;\b', '\b,\b');

my @array = (['input', 'port_a', ','],
             ['output', '[31:0]', 'port_b,', 'port_c', ',']);

To remove the patterns contained in @del_pattern from @array, I loop through all the elements in @del_pattern and exclude them using grep.

## delete the patterns found in @del_pattern array
foreach $item (@del_pattern) {
    foreach $i (@array) {
        @$i = grep(!/$item/, @$i);
    }
}

However, I have been unable to remove ',' from @array. If I use ',' instead of '\b,\b' in @del_pattern, element port_b, gets removed from the @array as well, which is not an intended outcome. I am only interested in removing elements that contain only ','.

Try using '^\,$' instead for removing the words having only , as the pattern you are using will remove all words having , anywhere in them. — Mohit
– Mohit, Commented May 17, 2017 at 5:32
So if you had input_a in @array should that get removed? In other words, do patterns need to match or to be equal? For the comma you are saying that it should be equal -- "that contain only ," (my emphasis). — zdim
– zdim, Commented May 17, 2017 at 6:24
If I had input_a in @array, it shouldn't get removed. The patterns need to match — Jon J
– Jon J, Commented May 17, 2017 at 7:21
OK -- but not the comma? With it, you remove an element only when it is exactly the comma? If that is the case, it makes most sense to make that regex /^,$/, so that matching it means that it is equal. — zdim
– zdim, Commented May 17, 2017 at 7:30
Also, you should make your regex with qr/.../ (not just single quotes). — zdim
– zdim, Commented May 17, 2017 at 7:32

Mohit · Accepted Answer · 2017-05-17 05:51:55Z

3

You are using the wrong regular expression. I updated the code and tried it and its working fine. PFB the update code:

my @del_pattern = ('input', 'output', 'wire', 'reg', '\b;\b', '^,$');

my @array = (['input', 'port_a', ','],
             ['output', '[31:0]', 'port_b,', 'port_c', ',']); 
## delete the patterns found in @del_pattern array
foreach my $item (@del_pattern) {
    foreach my $i (@array) {
        @$i = grep(!/$item/, @$i);
    }
}

The only change made is in the Regex '\b,\b' to '^,$'. I don't have much info on \b but the regex I am suggesting is doing what you intend.

answered May 17, 2017 at 5:51

Mohit

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1 Comment

ikegami Over a year ago

^,$ will remove both , and ,␊. ^,\z is the correct solution.

ikegami · Accepted Answer · 2020-08-12 13:56:43Z

1

You want

^,\z

An explanation of what \b doesn't match at all follows.

\b

defines the boundary of a "word". It is equivalent to

(?<=\w)(?!\w) | (?<!\w)(?=\w)

so

\b,\b

is equivalent to

(?: (?<=\w)(?!\w) | (?<!\w)(?=\w) ) , (?: (?<=\w)(?!\w) | (?<!\w)(?=\w) )

Since comma is a non-word character, that simplifies to

(?<=\w),(?=\w)

So

'a,b' =~ /\b,\b/      # Match
','   =~ /\b,\b/      # No match

edited Aug 12, 2020 at 13:56

answered Aug 12, 2020 at 5:47

ikegami

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Comments

FrankTheTank_12345 · Accepted Answer · 2017-05-17 06:31:43Z

0

This works, but not very nice from the code. This code snippet also removes the ','

 my $elm = [];

sub extract {
   my $elm = shift;

   foreach my $del (@del_pattern) {
      $elm =~ s/$del//g;
      if ( $elm ) {
         return $elm;
      }
   }
}


foreach my $item (@array) {
    foreach my $i (@$item) {
        my $extract = extract($i);
        if ($extract) {
           push(@$elm, $extract);
        }
    }
}

print Dumper($elm);

Why your @array has array? Why not one big array?

edited May 17, 2017 at 6:31

answered May 17, 2017 at 5:46

FrankTheTank_12345

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1 Comment

Jon J Over a year ago

It is a nested array. The original array contains a list of lines, where a single line is an element. A line is then split with space as delimiter, which forms array within an array. I structured it such that it would be easier for me to trace if there is a bug

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