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xy.coords: Extracting Plotting Structures

xy.coords

R Documentation

Extracting Plotting Structures

Description

xy.coords is used by many functions to obtain x and y coordinates for plotting. The use of this common mechanism across all relevant R functions produces a measure of consistency.

Usage

xy.coords(x, y = NULL, xlab = NULL, ylab = NULL, log = NULL,
          recycle = FALSE, setLab = TRUE)

Arguments

`x, y`	the x and y coordinates of a set of points. Alternatively, a single argument `x` can be provided.
`xlab, ylab`	names for the x and y variables to be extracted.
`log`	character, `"x"`, `"y"` or both, as for `plot`. Sets negative values to `NA` and gives a warning.
`recycle`	logical; if `TRUE`, recycle (`rep`) the shorter of `x` or `y` if their lengths differ.
`setLab`	logical indicating if the resulting `xlab` and `ylab` should be constructed from the “kind” of `(x,y)`; otherwise, the arguments `xlab` and `ylab` are used.

Details

An attempt is made to interpret the arguments x and y in a way suitable for bivariate plotting (or other bivariate procedures).

If y is NULL and x is a

formula:: of the form yvar ~ xvar. xvar and yvar are used as x and y variables.
list:: containing components x and y, these are used to define plotting coordinates.
time series:: the x values are taken to be time(x) and the y values to be the time series.
matrix or data.frame with two or more columns:: the first is assumed to contain the x values and the second the y values. Note that is also true if x has columns named "x" and "y"; these names will be irrelevant here.

In any other case, the x argument is coerced to a vector and returned as y component where the resulting x is just the index vector 1:n. In this case, the resulting xlab component is set to "Index" (if setLab is true as by default).

If x (after transformation as above) inherits from class "POSIXt" it is coerced to class "POSIXct".

Value

A list with the components

`x`	numeric (i.e., `"double"`) vector of abscissa values.
`y`	numeric vector of the same length as `x`.
`xlab`	`character(1)` or `NULL`, the ‘label’ of `x`.
`ylab`	`character(1)` or `NULL`, the ‘label’ of `y`.

Examples

ff <- stats::fft(1:9)
xy.coords(ff)
xy.coords(ff, xlab = "fft") # labels "Re(fft)",  "Im(fft)"

with(cars, xy.coords(dist ~ speed, NULL)$xlab ) # = "speed"

xy.coords(1:3, 1:2, recycle = TRUE) # otherwise error "lengths differ"
xy.coords(-2:10, log = "y")
##> xlab: "Index"  \\  warning: 3 y values <= 0 omitted ..