I love awk. I used to be afraid of it, but I started using it just to pluck columns, and over a couple years actually started to grok it.

Also, I learned today that cat takes a -n option to prepend line numbers to the output! My solution ended up being

    cat -n faces.txt | sort -k2 -k1n | uniq -f1 | sort -nk1,1 | cut -f2-