R: Extract Something From a Sealevel Object

[[,sealevel-method {oce} | R Documentation

## Extract Something From a Sealevel Object

### Description

The `[[` method works for all `oce` objects, i.e. objects inheriting from `oce-class`. The purpose is to insulate users from the internal details of `oce` objects, by looking for items within the various storage slots of the object. Items that are not actually stored in the object can also be extracted, including derived data such as potential temperature, the units of measurement for the data, data-quality flags, etc.

### Usage

    ## S4 method for signature 'sealevel'
    x[[i, j, ...]]

### Arguments

`x` | A sealevel object, i.e. one inheriting from `sealevel-class`.
`i` | Character string indicating the name of item to extract.
`j` | Optional additional information on the `i` item.
`...` | Optional additional information (ignored).

### Details

A two-step process is used to try to find the requested information. First, a class-specific function tries to find it, but if that fails, then a general function is used (see next section).

### Details of the general method

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. 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). For example, `x[["salinityFlag"]]` returns a vector of salinity flags if `x` is a ctd object.

4. If `i` is `"sigmaTheta"`, then the value of `swSigmaTheta(x)` is returned. Similarly, `"sigma0"` returns `swSigma0(x)` and `"spice"` returns `swSpice(x)`. Note that these relate to seawater properties and only make sense for certain object types.

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.

If none of the above-listed conditions holds, then `NULL` is returned, without the issuance of a warning or error message. (This silent operation is employed so that `[[` will behave like the normal R version.)

### See Also

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`, `[[,landsat-method`, `[[,lisst-method`, `[[,lobo-method`, `[[,met-method`, `[[,oce-method`, `[[,odf-method`, `[[,rsk-method`, `[[,section-method`, `[[,tidem-method`, `[[,topo-method`, `[[,windrose-method`, `[[<-,adv-method`

Other things related to sealevel data: `[[<-,sealevel-method`, `as.sealevel`, `plot,sealevel-method`, `read.sealevel`, `sealevel-class`, `sealevelTuktoyaktuk`, `sealevel`, `subset,sealevel-method`, `summary,sealevel-method`

[Package oce version 1.1-1 Index]