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use Data::Dumper;
use strict;
...
my $arr = ['A -4 C','C -4 B','B -4 A','A -2 C','C -3 B'];
my @a = map {[split " ",$_]} @$arr;
print Dumper(\@a);

$VAR1 = [
          [
...
            'B'
          ]
        ];