The [[ method works for all oce objects, i.e.
objects inheriting from oce-class. The purpose,
as with the related replacement method, [[<-,
is to insulate users from the internal details of oce
objects, by looking for items within the various storage
slots of the object. Items not actually stored can also be
extracted, including derived data, units of measurement,
and data-quality flags.
The method uses a two-step process to try to find the
requested information. First, a class-specific function
is used to try to access the requested information (see
“Details of the specialized ... method”).
Second, if no match is found, a general function is used
(see ‘Details of the general method’). If neither
method can locates the requested item, NULL is returned.
# S4 method for tidem
[[(x, i, j, ...)A tidem object, i.e. one inheriting from tidem-class.
Character string indicating the name of item to extract.
Optional additional information on the i item.
Optional additional information (ignored).
A vector of the frequencies of fitted constituents is recovered
with e.g. x[["frequency"]]. Similarly, amplitude is
recovered with e.g. x[["amplitude"]] and phase with
e.g. x[["phase"]]. If any other string is specified, then
the underlying accessor [[,oce-method) is used.
If the specialized method produces no matches, the following generalized
method is applied. As with the specialized method, the procedure hinges
first on the value of i.
First, a check is made as to whether i names one of the standard
oce slots, and returns the slot contents if so. Thus,
x[["metadata"]] will retrieve the metadata slot,
while x[["data"]] and x[["processingLog"]] return
those slots.
Next, if i is a string ending in the
"Unit", then the characters preceding that string
are taken to be the name of an item in the data object, and a list
containing the unit is returned. This list consists of an item
named unit, which is an expression, and
an item named scale, which is a string describing the
measurement scale. If the string ends in " unit", e.g.
x[["temperature unit"]], then just the expression is returned,
and if it ends in " scale", then just the scale is returned.
Next, if i is a string ending in "Flag", then the corresponding
data-quality flag is returned (or NULL if there is no such flag).
For example, x[["salinityFlag"]] returns a vector of salinity
flags if x is a ctd object.
If none of the preceding conditions are met, a check is done
to see if the metadata slot contains an item with
the provided name, and that is returned, if so. A direct match
is required for this condition.
Finally, the data slot is checked to see if it contains
an item with the name indicated by i. In this case, a partial
match will work; this is accomplished by using pmatch.
If none of the above-listed conditions holds, then NULL is returned.
Other functions that extract parts of oce objects: [[,adp-method,
[[,adv-method,
[[,amsr-method,
[[,argo-method,
[[,bremen-method,
[[,cm-method,
[[,coastline-method,
[[,ctd-method,
[[,echosounder-method,
[[,g1sst-method,
[[,gps-method,
[[,ladp-method,
[[,lisst-method,
[[,lobo-method,
[[,met-method, [[,odf-method,
[[,rsk-method,
[[,sealevel-method,
[[,section-method,
[[,topo-method,
[[,windrose-method,
[[<-,adv-method
Other things related to tidem data: [[<-,tidem-method,
plot,tidem-method,
predict.tidem,
summary,tidem-method,
tidedata, tidem-class,
tidemAstron, tidemVuf,
tidem