R: Extracting Plotting Structures

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)

### 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.

### 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 `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`.

### See Also

`plot.default`, `lines`, `points` and `lowess` are examples of functions which use this mechanism.

### Examples

    xy.coords(stats::fft(c(1:9)), NULL)

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

    xy.coords(1:3, 1:2, recycle=TRUE)
    xy.coords(-2:10,NULL, log="y")
    ##> warning: 3 y values <=0 omitted ..

[Package grDevices version 2.15.1 Index]