Question

Getting next value in array

Asked by: Neil2526

I have an array called @positions.

I have a value called $cur_position.

I want to see if $cur_position exists in @positions, if it does, i want to use the next value as $next_position, else i want to use the first value as $next_position.

my $current_position = $row->{'position'};
my @positions = sort keys %list_ads;
if ( grep $_ eq $current_position,  @positions ) {
#Grab next value as my $next_position                
}else{
#Grab first value in array as $next position
}

                                  
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Asked On
2009-11-07 at 10:43:37ID24880731
Tags

perl

Topic

Perl Programming Language

Participating Experts
3
Points
500
Comments
4

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Answers

 

by: ozoPosted on 2009-11-07 at 17:14:15ID: 25768923

$next_position = 0;
$_ == $current_position and $next_position = $_ and last for 0..$#positions;
$next_position = $positions[$next_position];

 

by: Neil2526Posted on 2009-11-08 at 13:51:21ID: 25772099

ozo, i'm still a bit new to perl, can you explain a little what you did. this is a lot of short hand.

thanks!

 

by: Adam314Posted on 2009-11-08 at 16:22:53ID: 25772709

The same code, in less short-hand, and with comments, and a minor fix (I believe there was a minor bug in the code ozo gave):

### Set the variable $next_position to 0.  This is the default if the $current_position is not found
$next_position = 0; 
### Loop from 0 to the second-to-last element in the array @positions,
### setting $index to the value
for my $index (0..$#positions-1) {
    ### if the $index'th position matches $current_position
    if($positions[$index] == $current_position)
        #### set $next_position to the next element, and stop searching
        $next_position = $index+1;
        last;
    }
} 
### set $next_position to the content in $positions, instead of the index
$next_position = $positions[$next_position];
                                              
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by: whosbetterthanmePosted on 2009-11-09 at 05:47:34ID: 25775829

Maybe this will help in a more layman sort of way:

my @positions = ('red','green','blue');
my $cur_position = 'green';
my $next_position = '';
my $next = 0;

foreach my $pos(@positions) {

            if ($cur_position eq $pos) {
            $next_position = $next + 1;
            $next_position = $positions[$next_position];
            }
            $next++;
}

if ($next_position eq '') {
$next_position = $positions[0];
}
print $next_position;

20120131-EE-VQP-002

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