I noticed this morning an unexpected behaviour of .spct objects when manipulated using data.table syntax… they become data.table objects! Until I solve this problem please do not use data.table syntax for manipulating .spct objects. I will upload a bugfix release of package photobiology, after I make sure that all functions defined in the package behave as expected. This will happen later today or tomorrow.
[edited @ 14:14, 22 July 2014] This time the bug was not in the code I had written, but rather in the data.table package. The code has recently been corrected in the development version of data.table (1.9.3), but this version is not yet available through CRAN… I will most likely upload a binary archive of data.table 1.9.3 to the r4photo repository later today, and a new version of package photobiology marked as requiring this or later versions of data.table.