search for: substrata

Dear R users, I face to a nested pattern and despite the numerous examples in the help I am still confused. I sampled bugs in different habitats within sites which were within rivers themselves within different regions. The habitat correspond to different substrata (not systematically present in all sites). For rivers and sites, I have environemental variables (e.g. altitude and slope of the site, drainage area and geology of the river) and I have only 2 regions. Note that sometimes I have only one site per river. I would like to know the part of each spatia...