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

Hello.

I'd like to ask a question regarding arrays and using/changing their contents from a loop.

For example: 

@array = qw/v w x y z/;

for(1 .. $nn) {

# I was expecting the array to shift
# at every loop, and I could call on
# the first position every time.

print OUT $array[0] , "\n";

$slide = shift(@array);
push(@array, $slide);

}

[download]
Obviously the original array isn't changing.
Is this what one would refer to as a scope issue/problem?

Thank you.

-Baratski

Replies are listed 'Best First'.
Re: Pushing arrays around inside a loop ;-)
by davido (Cardinal) on Jan 06, 2005 at 08:07 UTC

    When I give $nn some value, and get rid of the 'OUT' filehandle, so that I can run the script you've posted, I find that it does what should be expected: If $nn is set to 11, for example, you get: 

    v
w
x
y
z
v
w
x
y
z
v

    [download]

    The array most certanly is being modified by shift and push, and the snippit you provided demonstrates that. What were you expecting? Maybe there is a scoping issue at work, but if there is, you haven't shown it to us.

    And more importantly, what is it that you're trying to do?


    Dave

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      Thanks guys. Actually I am getting the output that you got. Sorry I should have been more clear.

      This is what I'm looking to get from the array:

      v w x y z
      w x y z v
      x y z v w

      And so on... If I'm shifting the contents of the array, shouldn't the value of the first position change, ie; $array[0]?

      What I'm doing is working through 2 arrays, one not shown that simply repeats itself by resetting a counter. The other is the one I am having trouble with.

      I'm trying to do this:

      Employee1 v
      Employee2 w
      Employee3 x
      Employee4 y
      Employee5 z

      Employee1 w
      Employee2 x
      Employee3 y
      Employee4 z
      Employee5 v

      Employee1 x
      Employee2 y
      Employee3 z
      Employee4 v
      Employee5 w

      And so on... It's a rotation schedule that I'm working on for my crew.

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        Use modulo division and you dont have to modify the arrays at all.

        my @emps=map "employee_$_",1..5;
my @codes='v'..'z';
my $n=3;
for my $j (0..$n-1) {
  for my $i (0..$#emps) {
    print $emps[$i],":",$codes[($i+$j) % @codes],"\n";
  }
  print "\n";
}
__END__
employee_1:v
employee_2:w
employee_3:x
employee_4:y
employee_5:z

employee_1:w
employee_2:x
employee_3:y
employee_4:z
employee_5:v

employee_1:x
employee_2:y
employee_3:z
employee_4:v
employee_5:w

        [download]
        ---
        demerphq

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Re: Pushing arrays around inside a loop ;-)
by ColtsFoot (Chaplain) on Jan 06, 2005 at 08:04 UTC
    What results were you getting, what errors were output?
    The following code seems to work for me
    #!/usr/bin/perl -w
use strict;

my @array = qw/v w x y z/;

for(1 .. 5) {

# I was expecting the array to shift
# at every loop, and I could call on
# the first position every time.

print $array[0] , "\n";

my $slide = shift(@array);
push(@array, $slide);

}

    [download]
[reply]
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Re: Pushing arrays around inside a loop ;-)
by gube (Parson) on Jan 06, 2005 at 09:50 UTC

    Hi,

    Just try this, 

    @array = qw/v w x y z/;

for(0 .. $#array) {
    
$slide = shift(@array);
push(@array1, $slide);

}

print @array1;

    [download]

    o/p: vwxyz

    Regards,

    Gubendran.L

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