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Perl: match an array element and then copy the element of the PREVIOUS array (5 indexes back) to a new array

basically what I'm trying to do is search through a large text file to identify each element that says " not found ", and a copy that matches the id of the new list. I am fine with the first part of this, but what I can’t understand is how to then copy the array element exactly 5 indexes back (which is the identifier) ​​and copy it to another array.

I tried something like this,

$fastafile = 'HpHcTEST.txt';
open(FASTAFILE, $fastafile);
@seq = <FASTAFILE>;
my $fastaid;
foreach (@seq) {
    if ($_ =~ /\*\*\*\*\* No hits found \*\*\*\*\*/){
        $fastaid .= $_[-5];
    }
}

print "here are the IDs\n";
print $fastaid;

with tons of options [-5], but none of them worked. I can not find the documentation on how to return the link and get the previous item if a match is made. Does anyone know how to code for this?

.

+3
4

- @seq .

my @fastaid;

for (my $i = 0; $i < @seq; ++$i) {
    if ($seq[$i] =~ /\*\*\*\*\* No hits found \*\*\*\*\*/){
        push @fastaid, $seq[$i - 5] if $i >= 5;
    }
}

@fastaid,

print "Here are the IDs:\n";
print "  - $_\n" for @fastaid;


print "Here are the IDs:\n",
      map "  - $_\n", @fastaid;

brian d foy , .

my $id_offset = 5;
my @fastaid;

for ($id_offset .. $#seq) {
    if ($seq[$_] =~ /\*\*\*\*\* No hits found \*\*\*\*\*/){
        push @fastaid, $seq[$_ - $id_offset];
    }
}

" " perldata, $#seq @seq, .. , @seq , $id_offset .

regex-bind .

my $id_offset = 5;
my @fastaid;

for my $i ($id_offset .. $#seq) {
  for ($seq[$i]) {
    push @fastaid, $seq[$i - $id_offset]
      if /\*\*\*\*\* No hits found \*\*\*\*\*/;
  }
}

5.10

use feature 'switch';

# ...

my $id_offset = 5;
my @fastaid;

for my $i ($id_offset .. $#seq) {
  given ($seq[$i]) {
    when (/\*\*\*\*\* No hits found \*\*\*\*\*/) {
      push @fastaid, $seq[$i - $id_offset];
    }
  }
}

, $# ,

for (@fastaid) {
    if (/\*\*\*\*\* No hits found \*\*\*\*\*/) {
        push @fastaid, $seq[$# - 5] if $# >= 5;
    }
}

.

+3

:

for (5..$#seq) {
    $fastaid .= $seq[$_-5] if $seq[$_] =~ /your_regex/;
}

Perl 5.12 each:

while (my ($index, $value) = each @seq) {
    next if $index < 5;
    $fastaid .= $seq[$index-5] if $value =~ /your_regex/;
}
+3
my @fasta_id = map { $seq[$_] =~ /your_regex/ ? $seq[$_-5] : () } 5 .. $#seq;
+2
source

Use the 'for' loop instead of the 'foreach',

for ($index=0; $index < $#seq + 1; $index++) {
    if ($seq[$index] =~ /\*\*\*\*\* No hits found \*\*\*\*\*/){
        $fastaid .= $seq[$index-5];
    }
}
-2
source

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