R: Extracting Plotting Structures

xy.coords {base} | R Documentation

## Extracting Plotting Structures

### Description

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

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

### Usage

    xy.coords(x, y, 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 be provided. In this case, an attempt is made to interpret the argument in a way suitable for plotting. If the argument is a formula `yvar ~ xvar`, `xvar` and `yvar` are used as x and y variables; if the argument is a list containing components `x` and `y`, these are used are assumed to define plotting coordinates; if the argument contains a time series, the x values are taken to be time and the y values to be the time series; if the argument is a matrix with two columns, the first is assumed to contain the x values and the second the y values; in any other case, the argument is coerced to a vector and the values plotted against their indices.
`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.

### 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

    xy.coords(fft(c(1:10)), NULL)
    data(cars) ; attach(cars)
    xy.coords(dist ~ speed, NULL)$xlab # = "speed"

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

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