How about this? It seems to do you what you want, at least for the given test data.

use v5.16;
use warnings;

# collapse a list 

my @data = (0, 3, 8, 9, 5, 2, 0, 1, 0);

my $acc = 0;

say join(',',@data);

while (@data && $data[0] < 5) {
  $acc += shift @data;
}
$data[0] += $acc;

$acc = 0;
while (@data && $data[$#data] < 5) {
  $acc += pop @data;
}
$data[$#data] += $acc;


say join(',',@data);

[download]

BUT, what do you want to happen if the accumulated total become more than 5? i.e if the list starts (2,2,2,7,...) should the result be (13,...) or (6,7,...) or don't you care?

In reply to Re: sum towards nearest good neighbor at either end of numerical array by RichardK
in thread sum towards nearest good neighbor at either end of numerical array by rgart

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