This assumes unimodal datasets:

sub mode{ 
    my %h; ++$h{ $_ } for @_; 
    return ( sort{ $h{ $b } <=> $h{ $a } } keys %h )[ 0 ] 
};;

@data = qw[2 3 3 3 5 7 8 12 32 44 55 12 3 23 43 33 1 4 25 43 42 1 4 5 
+3 3 3];;

print mode( @data );;
3
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You'd need to so a bit more work to discover bi/multimodal datasets.