Reference

All functions
colmean_group_apply()	Compute the mean spectra per group label for all spectra in a collection
ids_apply()	Add atomic vector labels for row, id and group for all rows of spectra.
sg_apply()	Combinatory Savitzky-Golay Filtering
sg_make_plan()	Generate a data.frame with Savitzky-Golay parameters
snv_apply()	Compute the standard normal variate for collections of spectra