Re^4: Using an array element as a loop iterator

Thanks. That is nice

for (@b){$a[1]=$_;say:}
[download]

But what I actually wanted to achieve was that I had several nested foreach loops and taking several variables, one for each iterator, is nearly horrible. I wanted to initialize one array and then use that as a container for all the iterators of nested arrays.

This step $a[1]=$_or something similar will do that, but still that statement needs to be put as first step in loops of all 20 nested arrays. Isn't there any way through which we can avoid that and achieve the result via the foreach step only like something --

my @a=();
foreach $a[0](`cat file`){
 foreach $a[1](@b){
  foreach $a[2](grep (/4/, @c)){
   <More statements>
}}}
[download]

And not using something like--

my @a=();
foreach (`cat file`){
 $a[0]=$_;
 foreach $a[1](@b){
  $a[1]$_;
  foreach $a[2](grep (/4/, @c)){
   $a[2]=$_
   <More statements>
}}}
[download]

</code>

Comment on Re^4: Using an array element as a loop iterator Select or Download Code

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Re^5: Using an array element as a loop iterator by AnomalousMonk (Archbishop) on Nov 08, 2013 at 16:27 UTC
It sounds as if you might want something like Algorithm::Loops`::NestedLoops` (among many similar on CPAN): >perl -wMstrict -le "my $number = 99; my $letter = 'Z'; my $word = 'zot'; ;; my @words= qw(foo bar); ;; for my $number (1 .. 3) { for my $letter (qw(A B C)) { for my $word (@words) { do_something_with($number, $letter, $word); } } } ;; print qq{post-loop: '$number' '$letter' '$word' \n} ;; sub do_something_with { my (@args) = @_; ;; print qq{@args}; } ;; ;; use Algorithm::Loops qw(NestedLoops); ;; print qq{using NestedLoops:}; NestedLoops [ [ 1 .. 3 ], [ qw(A B C) ], \@words, ], \&do_something_with ; " 1 A foo 1 A bar 1 B foo 1 B bar 1 C foo 1 C bar 2 A foo 2 A bar 2 B foo 2 B bar 2 C foo 2 C bar 3 A foo 3 A bar 3 B foo 3 B bar 3 C foo 3 C bar post-loop: '99' 'Z' 'zot' using NestedLoops: 1 A foo 1 A bar 1 B foo 1 B bar 1 C foo 1 C bar 2 A foo 2 A bar 2 B foo 2 B bar 2 C foo 2 C bar 3 A foo 3 A bar 3 B foo 3 B bar 3 C foo 3 C bar [download] With this approach it's easy to add arrays to arbitrary depth, albeit with attendant exponential explosion! Update: Changed example code to show `\@words` taking reference to array.	[reply] [d/l] [select]
Re^5: Using an array element as a loop iterator by Eily (Monsignor) on Nov 08, 2013 at 17:14 UTC
Oh, it's far clearer with the nested loops example ^^. You could also do: for(@a1=`cat file`;$a[0]=shift @a1;@a1) { for(@a2=@b;$a[1]=shift @a2;@a2) # could be "for(;$a[1]=shift @b;@b)" + if you don't care about emptying @b { for(@a3=grep /4/, @c;$a[2]=shift @a3;@a3) { <Statements>; } } } [download] but that's kind of ugly. Maybe you could use that with source filtering to have a lighter syntax ... If you intend to do that sort of things often in your script you could use Perl Prototypes to add that kind of syntax to your program: `sub with {for (@{$_[1]}){$_[0] = $_;$_[2]();}} sub in { \@_ } sub run(&) { $_[0] }` [download] Then you could write : `# parenthesis mandatory after in, bad idea after with and the commas c +an't be ommited with $a[0], in(qw/Bonjour Bonsoir/), run { with $a[1], in ("Paul", "Jack", "Lord Voldemort"), run { say "@a"; }; # semi-colon mandatory }; # same here` [download] `Bonjour Paul Bonjour Jack Bonjour Lord Voldemort Bonsoir Paul Bonsoir Jack Bonsoir Lord Voldemort` [download] But I did that because it was fun, and a bit of a challenge, but that's not very practical. You probably have to stick with my first answer.	[reply] [d/l] [select]
Re^6: Using an array element as a loop iterator by LanX (Saint) on Nov 08, 2013 at 19:45 UTC
> but that's kind of ugly. maybe easier written with while loops? `while ($a[0] =shift @a1) { ... }` ... well at least for me better readable :) Cheers Rolf ( addicted to the Perl Programming Language)	[reply] [d/l]
Re^7: Using an array element as a loop iterator by Eily (Monsignor) on Nov 08, 2013 at 20:14 UTC
It surely is ^^. The problem is that you can't use that construct like this: while( $a[0] = shift `cat file` ) (but that is a unusual way to read a file, indeed). So you do have to set @a1 first, which is the first part of my for loop. And if @a1 contains a value that is false, `$a[0] = shift @a1` will be false as well, so the loop will stop early. `defined($a[0] = shit @a1)` would work, unless you want to use undef as a value. That's why I used @a1 in scalar context as the third part of the for loop.	[reply] [d/l] [select]
Re^8: Using an array element as a loop iterator by LanX (Saint) on Nov 08, 2013 at 20:19 UTC
Re^7: Using an array element as a loop iterator by gurpreetsingh13 (Scribe) on Nov 09, 2013 at 08:59 UTC
Thanks a lot. Got the point.	[reply]