Problems with dps

[hhwagner1]

Please check the data 'dps':

• There is a weird pattern of zero's.
• Values seem incompatible with the log-transformed dps values in ralu.models
• Incompatibility issue with 'LandGenCourse', Week 13 vignette: dps does not have attributes 'FROM_SITE', 'TO_SITE' anymore, which are needed on line 122-123 for merging:
  dps$from.to <- paste(dps$FROM_SITE, dps$TO_SITE, sep=".")
  dist.graph <- merge(dist.graph, dps, by = "from.to")