Select a portion of an glider object, specified according to one
of several possible schemes, based on the form of the argument named
subset. Note that the schemes cannot be combined, so
nested calls must be used to accomplish combinations.
Usage
# S4 method for class 'glider'
subset(x, subset, ...)Arguments
- x
an oceglider object, i.e. one inheriting from the glider.
- subset
a logical expression or a character string that indicates how to take the subset. See “Details”.
- ...
Additional arguments, of which the only one permitted at the moment is
debug, an integer indicating the level of debugging information to be permitted.
Details
Scheme 1: if subset is a logical expression written
in terms of data that are stored in the yos, then this expression is applied
to the payload1 item in the data slot of the object
(see Example 1).
Scheme 2: if subset is a logical expression containing
the word "yolength", then the expression is used as a filter
to select yos based on the number of samples they
contain (see Example 2). Typically, this might be used to avoid
very short yos that might have been inferred erroneously
by the glider instrumentation.
Scheme 3: If subset is the string "ascending", then
only ascending segments of yos are retained. This is done
by selecting for navState==117 in both the glider
and payload1 streams of the data slot of the object.
Scheme 4: If subset is the string "descending", then
only descending segments of yos are retained. This is done
by selecting for navState==100 in both the glider
and payload1 streams of the data slot of the object.
Bugs
The 'ascending' and 'descending' methods do not work. This seems to be a problem of exporting classes using roxygen2 tags. I am looking into this. DK 2019-03-28.
Examples
if (FALSE) { # \dontrun{
# Example 1. remove wild salinities
library(oceglider)
g <- read.glider(filename)
gg <- subset(g, 0 < salinity & salinity < 40)
par(mfrow = c(2, 1))
hist(g[["salinity"]], main = "S original")
hist(gg[["salinity"]], main = "S cleaned")
# Example 2. remove short yos
gg <- subset(g, yolength > 4)
# Example 3. retain only ascending portions of yos
gascending <- subset(g, "ascending")
# Example 4. retain only descending portions of yos
gdescending <- subset(g, "descending")
} # }