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my @arr = (['a','b','c'],
           ['h','i','j'],
           ['x','y','z']);

my @first_column = map $_->[0], @arr;

my @arr = (['a','b','c'],
           ['h','i','j'],
...
for (map $_->[0], @arr) {
   # $_ now holds the current value of column 1 (index 0)
}