getting iteration number inside iteration loop

jesuashok has asked for the wisdom of the Perl Monks concerning the following question:

monks,

Apologies if this has been discussed already.

my $iteration_number = 1;
foreach my $val ( @array ) {
   print ":$iteration_number:\n";
   $iteration_number ++;
}
[download]

In the above code to get the iteration number I am using a explicit flag to get the iteration count. I am interested to know, is there any built-in variable available to hold the iteration count ? For example $. holds the line number during the any FILEHANDLING operation.

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Re: getting iteration number inside iteration loop by blazar (Canon) on Jun 29, 2007 at 07:36 UTC
Yes, this has been discussed ad nauseam and no, there's not such a variable. Hence one should either maintain a counter like you did or, when the actual list happens to be an array as in your example, despite the appeal of iterating over an `@array` with aliasing to its elements, just iterate over `0..$#array` and use subscripting.	[reply] [d/l] [select]
Re^2: getting iteration number inside iteration loop by jesuashok (Curate) on Jun 29, 2007 at 08:12 UTC
Thanks to GrandFather and blazar for confirming this.	[reply]
Re: getting iteration number inside iteration loop by GrandFather (Saint) on Jun 29, 2007 at 07:34 UTC
There is not. BTW, if you: `my $iteration_number = 0; foreach my $val ( @array ) { $iteration_number ++; print ":$iteration_number:\n"; }` [download] then you know how may times the loop was entered by inspecting $iteration_number after the loop has completed. DWIM is Perl's answer to Gödel	[reply] [d/l]
Re: getting iteration number inside iteration loop by ikegami (Patriarch) on Jun 29, 2007 at 13:19 UTC
You probably want `for my $i ( 0 .. $#array ) { print "$i: $array[$i]\n"; }` [download] Note that a `for`/`foreach` loop that loops over `x..y` is very effecient. `x..y` doesn't get flattened into a list as it would elsewhere.	[reply] [d/l] [select]
Re: getting iteration number inside iteration loop by ferreira (Chaplain) on Jun 29, 2007 at 14:47 UTC
You may get this behavior with List::MoreUtils. The following presents two such solutions. They are not very pretty, but they work. First, you may generate an index array with `[ 0 .. $#array ]` and use `each_arrayref/each_array` to produce an iterator that loops over possibly many arrays at a time. `use List::MoreUtils qw( each_arrayref ); my @a = qw( a b c d e ); my $each = each_arrayref( [ 0..$#a ], \@a ); while ( my ($idx, $v) = $each->() ) { print "$idx: $v\n"; }` [download] Second, you may use the documented behavior that the iterator returns the current index when given arguments `('index')`. `use List::MoreUtils qw( each_array ); my @a = qw( a b c d e ); my $each = each_array( @a ); while ( my $v = $each->() ) { my $idx = $each->('index'); print "$idx: $v\n"; }` [download]	[reply] [d/l] [select]