Suppose we have a crystal in the form of a rectangular block, given by a list of the absolute atomic coordinates with one atom per line Ga -9.278018850000 -9.642000000000 -7.870137870000 N -7.422415050000 -9.642000000000 -8.518637230000 . . . looking like that:  What we really want, though, is a hexagonal column which tapers down from the bottom to the top — just like a column of [Doric order](http://en.wikipedia.org/wiki/Doric_order). How can we sculpt this column out of the block we have? Where do we get the digital chisel we need? A [colleague of mine](https://scholar.google.de/citations?user=p3b43FsAAAAJ&hl=en&pagesize=100) solved this quest in the most elegant fashion: with an awk one-liner. awk '{x=sqrt($2^2);y=sqrt($3^2);d=x/2+sqrt(3)/2*y;z=$4;cutoff='$radius1'*('$zmax'-z)/'$zrange'+'$radius2'*(z-('$zmin'))/'$zrange'};d<=cutoff && x column.dat Voilà: