# xy.coords: 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

 ```1 2``` ```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`.

`plot.default`, `lines`, `points` and `lowess` are examples of functions which use this mechanism.
 ```1 2 3 4 5 6 7 8 9``` ```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 .. ```