xy.coords {grDevices}  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 
xlab , ylab 
names for the x and y variables to be extracted. 
log 
character, 
recycle 
logical; if 
setLab 
logical indicating if the resulting 
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
andyvar
are used as x and y variables. list:
containing components
x
andy
, 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., 
y 
numeric vector of the same length as 
xlab 

ylab 

See Also
plot.default
, lines
, points
and lowess
are examples of functions which use this mechanism.
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)$xlab ) # = "speed"
xy.coords(1:3, 1:2, recycle = TRUE) # otherwise error "lengths differ"
xy.coords(2:10, log = "y")
##> xlab: "Index" \\ warning: 3 y values <= 0 omitted ..
op < options(warn = 2)# ==> warnings would be errors, we suppress the one "we know":
suppressWarnings(xy.coords(2:10, log = "y"), classes="log_le_0") > xy
options(op) # revert
stopifnot(is.list(xy), identical (1:13 +0, xy$x),
identical(c(rep(NA, 3), 1:10 +0), xy$y))