use PDL::VectorValued::Utils;
# $pdl is ncoords=3,nvertices=3,ntriangles
my $uniqv = $pdl->uniqvec; # ncoords=3,nunique
my $face_indices = vsearchvec($pdl, $uniqv); # nvertices=3,ntriangles

##</code><code>##

$cube->indexND($coords) .= $count;

##</code><code>##

pdl> $photon_list = new PDL::RandVar->sample(500)->reshape(2,250)*10
pdl> $histogram = zeroes(10,10)
pdl> $histogram->range($photon_list,1)++;  #not what you wanted