to expand a bit on broquaint's answer, use the following to place your vertical 'slice' into an array:

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

my @first_column = map $_->[0], @arr;
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or if you'd like to simply skip that step, and go straight to iterating over them:

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

for (map $_->[0], @arr) {
   # $_ now holds the current value of column 1 (index 0)
}
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hope that helps.