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Generally, the [[ method lets users extract information from oce objects, without having to know the details of the internal storage. For many oce sub-classes, [[ can also return quantities that are computed from the object's contents.


# S4 method for class 'adp'
x[[i, j, ...]]



an adp object.


character value indicating the name of an item to extract.


optional additional information on the i item.




A two-step process is used to try to find the requested information. First, a class-specific function is used (see “Details of the Specialized Method”). If this yields nothing, then a general method is used (see “Details of the General Method”). If both methods fail, then [[ returns NULL.

Some understanding of the subclass is required to know what can be retrieved with [[. When dealing with an unfamiliar subclass, it can be useful to first use x[["?"]] to get a listing of the retrievable items. See “Details of the Specialized Method” for more information.

Details of the Specialized Method

Note that the entries within adp objects vary greatly, from instrument to instrument, and so are only sketched here, and in the output from [["?"]].

  • If i is "?", then the return value is a list containing four items, each of which is a character vector holding the names of things that can be accessed with [[. The data and metadata items hold the names of entries in the object's data and metadata slots, respectively. The dataDerived and metadataDerived items are not authoritative, because information provided by different instruments is so varied.

  • If i is "u1" then the return value is v[,1]. The same holds for 2, etc., depending on the number of beams in the instrument.

  • If i is "a1" then signal amplitude is returned, and similarly for other digits. The results can be in raw() or numeric form, as shown in the examples.

  • If i is "q1" then signal quality is returned, and similarly for other digits. As with amplitude, the result can be in raw() or numeric form.

  • If i is "coordinate", then the coordinate system is retrieved.

Details of the General Method

Note: the text of this section is identical for all oce subclasses, and so some of what you read here may not be relevant to the class being described in this help page.

If the specialized method produces no matches, the following generalized method is applied. As with the specialized method, the procedure hinges first on the values of i and, optionally, j. The work proceeds in steps, by testing a sequence of possible conditions in sequence.

  1. A check is made as to whether i names one of the standard oce slots. If so, [[ returns the slot contents of that slot. Thus, x[["metadata"]] will retrieve the metadata slot, while x[["data"]] and x[["processingLog"]] return those slots.

  2. 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 (or NULL if there is no such unit). 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"]] (note the space), then just the expression is returned, and if it ends in " scale", then just the scale is returned.

  3. If i is a string ending in "Flag", then the corresponding data-quality flag is returned (or NULL if there is no such flag).

  4. If the object holds hydrographic information (pressure, salinity, temperature, longitude and latitude) then another set of possibilities arises. If i is "sigmaTheta", then the value of swSigmaTheta() is called with x as the sole argument, and the results are returned. Similarly, swSigma0() is used if i="sigma0", and swSpice() is used if i="spice". Of course, these actions only make sense for objects that contain the relevant items within their data slot.

  5. After these possibilities are eliminated, the action depends on whether j has been provided. If j is not provided, or is the string "", then i is sought in the metadata slot, and then in the data slot, returning whichever is found first. In other words, if j is not provided, the metadata slot takes preference over the data slot. However, if j is provided, then it must be either the string "metadata" or "data", and it directs where to look.

  6. If none of the above-listed conditions holds, then NULL is returned.


Dan Kelley


# Tests for beam 1, distance bin 1, first 5 observation times
adp[["v"]][1:5, 1, 1]
#> [1] -0.11955771 -0.09925398  0.10203802  0.09613003  0.24394126
adp[["a"]][1:5, 1, 1]
#> [1] 99 9d 9f 87 8a
adp[["a", "numeric"]][1:5, 1, 1]
#> [1] 153 157 159 135 138
as.numeric(adp[["a"]][1:5, 1, 1]) # same as above
#> [1] 153 157 159 135 138