This function is somewhat analogous to subset.data.frame.
# S4 method for odf
subset(x, subset, ...)an odf object.
a condition to be applied to the data portion of
x.  See ‘Details’.
ignored.
A new odf object.
It seems likely that users will first convert the odf object into another class (e.g. ctd) and use the subset method of that class; note that some of those methods interpret the … argument.
Other things related to odf data: ODF2oce,
  ODFListFromHeader,
  ODFNames2oceNames,
  [[,odf-method,
  [[<-,odf-method, odf-class,
  plot,odf-method,
  read.ctd.odf, read.odf,
  summary,odf-method
Other functions that subset oce objects: subset,adp-method,
  subset,adv-method,
  subset,amsr-method,
  subset,argo-method,
  subset,cm-method,
  subset,coastline-method,
  subset,ctd-method,
  subset,echosounder-method,
  subset,lobo-method,
  subset,met-method,
  subset,oce-method,
  subset,rsk-method,
  subset,sealevel-method,
  subset,section-method,
  subset,topo-method