Deleting elements of one list using another

[Sj03rd]

Greetings to you, oh great Monks

I would like to compare two arrays and keep only those elements that PARTIALLY intersect. For example, let the two array's be:

@arr1 = ("0000007 | John | ABC.txt | 42","0000014 | Jane | XYZ.txt | 34","0000017 | Jessica | GHI.txt | 21", etc);
@arr2 = (0000007, 0000014);
This should result in a text file arr3.dat that contains something like
0000007 | John | ABC.txt | 42
0000014 | Jane | XYZ.txt | 34

I know I should use hashes and know how to split element-by-element but can't figure this one out.

EDIT: CODE ADDED, SORRY FOR BEING UNSPECIFIC. THE FINAL ROW SUGGESTS THAT THE HASHING GOES WRONG...
EDIT AGAIN: SOLUTION BY nemesdani WORKS FINE (BUT SEE MY REPLY).
Thanks!

use feature ':5.10';

open (KEYFILE, "arr2.txt");
    @arr2 = <KEYFILE>;
close(KEYFILE);

# Declare and fill up the hash
my %elements;
foreach (@arr2) {
    $elements{$_} = 1;
};

#I'm repeating this for several quarterly files:
for($year=2006; $year<2012; $year=$year+1){
    for($i=1; $i<5; $i=$i+1){
    
        # Load each quarterly file
        $filea = $year . "QTR" . $i . "arr1.txt";
        open(MYINFILE, $filea);
            @arr1 = <MYINFILE>;
        close(MYINFILE);
        $sizegn = @arr1;

        # For each entry in the quarterly file
        for($j=0; $j<$sizegn; $j++){
            
            # Pick only lines that contain the string "txt"
            if($arr1[$j] =~ m/txt/){
            
                # splits the elements of @arr1, and format the first e
+lement into 7-digit number:
                @arraydata = split(/\|/, $arr1[$j]); 
                my $element = sprintf("%07d", $arraydata[0]); 
                
                # now check if $element is in hash :
                if (exists $elements{$element}){
                    open(MYOUTFILE, ">>Arr3.dat");
                    print MYOUTFILE $arr1[$j];
                    close(MYOUTFILE);
                }
                print "D'oh - '$element' not found\n" unless (exists $
+elements{$element});
            }
        }
    }
}

[Anonymous Monk]

I know I should use hashes and know how to split element-by-element but can't figure this one out.

Figure what out, exactly (be specific)?

Anyway, its FAQ

$ perldoc -q duplicate

perlfaq4 How can I remove duplicate elements from a list or array?

$ perldoc -q substring

perlfaq4 How can I count the number of occurrences of a substring within a string?

Also see perlintro#Regular expressions the Simple matching paragraph

[nemesdani]

Untested and unnecessary verbose, but I think you'll get the idea:



use strict;
use warnings;

my @arr1 = ("John, ABC, 42","Jane, XYZ, 34","Jessica, GHI, 21");
my @arr2 = ("ABC", "XYZ");
my @arr3;
my %seen;
foreach my $arr1(@arr1) {

    my @splitted = split (/,/, $arr1);
    foreach my $arr2(@arr2) {
        if (grep(/$arr2/, @splitted)) {
            unless ($seen{$arr1} ){
                push (@arr3, $arr1);
            }
        }
    }
}

for (@arr3) {print "$_\n";}

[Sj03rd]

Great, this works fine for me. Flawless code except for  @splitted in the  grep command which should be  @splitted[0]. Thanks!

[nemesdani]

You mean $splitted[0]? :)
But no. splitted[0] contains "John" in the first loop, than "Jane", finally "Jessica". You'd like to grep the whole "John ABC 42" for ABC, don't you?
Otherwise I haven't understand the problem well enough.

[jwkrahn]

$ perl -le'
use Data::Dumper;
my @arr1 = ( "John, ABC, 42", "Jane, XYZ, 34", "Jessica, GHI, 21" );
my @arr2 = ( "ABC", "XYZ" );
my $pattern = join "|", @arr2;
my @arr3 = grep /$pattern/, @arr1;
print Dumper \@arr3;
'
$VAR1 = [
          'John, ABC, 42',
          'Jane, XYZ, 34'
        ];

[suaveant]

Right idea but you aren't using anything to anchor the pattern, so you would also match 'JohnABC, CDE, 14'

@arr1 = ("0000007 | John | ABC.txt | 42","0000014 | Jane | XYZ.txt | 3
+4","0000017 | Jessica | GHI.txt | 21", etc);
@arr2 = ('0000007', '0000014');

my $re = join('|',@arr2);
my @arr3 = grep /^(?:$re)\s/, @arr1;

print join("\n",@arr3),"\n";

[aaron_baugher]

In pseudo-code:

make a hash of @arr2
instantiate @arr3
for each element of @arr1
  split it to get the second field
  if that field is a key in the hash
    push the element onto @arr3