How can increase number sequence in a variable

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

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Re: How can increase number sequence in a variable by haukex (Archbishop) on Nov 17, 2017 at 16:21 UTC
It's theoretically possible, but "it's stupid to use a variable as a variable name". Usually, a hash is what you want, since the keys are strings that you could compose out of other variables. In this case though, it sounds like what you want is an array of arrays. (Update: See also perllol) `use warnings; use strict; use Data::Dump; my @A; for my $i (0..5) { $A[$i][0] = 1234; } dd @A; __END__ ([1234], [1234], [1234], [1234], [1234], [1234])` [download]	[reply] [d/l]
Re: How can increase number sequence in a variable by 1nickt (Canon) on Nov 17, 2017 at 16:34 UTC
Hi, welcome. Please see Where should I post X? (I moved your post into the correct section) How do I post a question effectively? Markup in the Monastery The instructions right next to the 'Preview' button Also see: perlintro for Why it's stupid to use a variable as a variable name perlreftut When you pass arrays to a loop each element will be handled separately. `perl -Mstrict -wE 'my @x=1..2; my @y=3..4; say "$_" for (@x, @y);' 1 2 3 4` [download] If you want the arrays to be handled as units, you must pass a reference to them instead: `perl -Mstrict -wE 'my @x=1..4; my @y=1..4; say "$_" for (\@x, \@y);' ARRAY(0xcd9588) ARRAY(0xcd9510)` [download] If you then want to access the elements of the individual arrays you will have to dereference them in the loop: `perl -Mstrict -wE 'my @x=1..2; my @y=3..4; say "@{$_}" for (\@x, \@y); +' 1 2 3 4` [download] Hope this helps! The way forward always starts with a minimal test.	[reply] [d/l] [select]
Re^2: How can increase number sequence in a variable by karlgoethebier (Abbot) on Nov 17, 2017 at 18:09 UTC
"...pass a reference" It depends... `perl -Mstrict -E 'my @x=(1..2); my @y=(3..4); say join ",", map{$_} (@x,@y)'` Best regards, Karl ŤThe Crux of the Biscuit is the Apostropheť `perl -MCrypt::CBC -E 'say Crypt::CBC->new(-key=>'kgb',-cipher=>"Blowfish")->decrypt_hex($ENV{KARL});'`Help	[reply] [d/l] [select]
Re^3: How can increase number sequence in a variable by 1nickt (Canon) on Nov 17, 2017 at 21:30 UTC
Hi kgb, I'm not certain what you are intending to show there. As I understood it the OP wanted to keep the arrays separated in the loop. And if they are to be contatenated with `join`, you don't need `map`. `perl -Mstrict -E 'my @x=(1..2); my @y=(3..4); say join "->", (@x,@y)' 1->2->3->4` [download] The way forward always starts with a minimal test.	[reply] [d/l] [select]
Re^4: How can increase number sequence in a variable by karlgoethebier (Abbot) on Nov 18, 2017 at 10:37 UTC
Re: How can increase number sequence in a variable by AnomalousMonk (Archbishop) on Nov 17, 2017 at 23:05 UTC
Just so you'll know what not to do, here's what you asked for in the OP: `c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le "our @A_0; our @A_1; our @A_2; our @A_3; ;; for my $i (0 .. 3) { my $name = qq{A_$i}; no strict 'refs'; $name->[$i] = 1000 + $i; } dd \@A_0; dd \@A_1; dd \@A_2; dd \@A_3; " [1000] [undef, 1001] [undef, undef, 1002] [undef, undef, undef, 1003]` [download] This works with strict (and warnings) fully enabled, but only by invoking `no strict 'refs'` just before things go sideways. ~~This~~ \| Soft referencing only works with package global variables, one of the drawbacks of soft referencing. In the example, our is used to declare the package global arrays. Note that the `my $name = qq{A_$i};` statement could be eliminated and the reference could be taken directly from the constructed string: `qq{A_$i}->[$i] = 1000 + $i;` (I use Data::Dump`::dd()` because I like it, but it's not core. Data::Dumper is core.) Much better practice is the use of hard references: `c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le "my @A_0; my @A_1; my @A_2; my @A_3; ;; for my $arrayref ( \(@A_0, @A_1, @A_2, @A_3) ) { $arrayref->[0] = 1234; } dd \@A_0; dd \@A_1; dd \@A_2; dd \@A_3; " [1234] [1234] [1234] [1234]` [download] Note that the variables being operated on are my (or lexical) variables, but the same referencing mechanism works with package globals (our variables) as well. Note also the `\(@ra, @rb, ...)` syntax for taking hard references to a collection of (any mixture of) variables. This is just a convenience, and the loop could just as well have been defined `for my $arrayref (\@A_0, \@A_1, \@A_2, \@A_3) { ... }` The `\( ... )` device can be used in conjunction with the declaration of a set of variables and the list of references taken can be captured in an array. The set of references in this array can then be operated on as a group. Note that the `\my ( ... )` device can be used only to declare and not to initialize variables. The lexical variables created in the `my (@A_0, @foo, @A_2, @A_3)` expression below behave just like any lexical; they could also be our variables. `c:\@Work\Perl\monks>perl -wMstrict -MData::Dump -le "my @arrayrefs = ( \my (@A_0, @foo, @A_2, @A_3) ); ;; for my $i (0 .. $#arrayrefs) { $arrayrefs[$i][$i] = 1000 + $i; } dd \@A_0; dd \@foo; dd \@A_2; dd \@A_3; " [1000] [undef, 1001] [undef, undef, 1002] [undef, undef, undef, 1003]` [download] (Update: The `my @arrayrefs = ( \my (@A_0, @foo, @A_2, @A_3) );` statement could be written slightly more simply as `my @arrayrefs = \my (@A_0, @foo, @A_2, @A_3);` since the outermost `( )` grouping is unnecessary.) A reference to the `@arrayrefs` array could be taken and passed around, etc., etc. Use your imagination — but don't use soft references (without a very good reason, but you didn't hear me say that). Update: And here's yet another variation that uses each to simultaneously iterate over the indices and elements of the `@arrayrefs` array (needs Perl version 5.12+): `c:\@Work\Perl>perl -wMstrict -MData::Dump -le "use 5.012; ;; my @arrayrefs = \my (@A_0, @foo, @A_2, @A_3); ;; while (my ($i, $ar) = each @arrayrefs) { $ar->[$i] = 1000 + $i; } dd \@A_0; dd \@foo; dd \@A_2; dd \@A_3; " [1000] [undef, 1001] [undef, undef, 1002] [undef, undef, undef, 1003]` [download] Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]
Re: How can increase number sequence in a variable by AnomalousMonk (Archbishop) on Nov 17, 2017 at 17:06 UTC
For future reference, what you want to do is to use a "symbolic" or "soft" reference; see perlref. And yes, this is Officially Frowned Upon and yes, you probably want to use a hash or some other "hard" referencing scheme; see also perldsc. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l]