callArg: Work with plot call arguments

Description

Part of the playwith Application Programming Interface.

Usage

callArg(playState, arg, eval = TRUE, data = NULL)
callArg(playState, arg) <- value
mainCall(playState)
mainCall(playState) <- value
updateMainCall(playState)

Arguments

playState

a playState object representing the plot, window and device.

arg

the argument name or number in the main plot call. This can also be a language object (e.g. quote(scales$log)). Argument numbers start from 1 (so 0 refers to the main function name). This is evaluated in the calling environment, so can refer to local variables (e.g. data[[myname]]).

eval

whether to evaluate the argument before returning it. Otherwise, just return the argument as it appears in the call.

data

a list or environment in which to evaluate the argument. Typically this will be the "data" argument to lattice or qplot functions.

value

the value to assign.

Value

returns the value of the specified argument, possibly evaluated in a local environment (playState$env).

Details

These functions get and set argument values in the playState plot call.

As convenience functions for setting arguments in playState$call, the callArg function helps by:

referring to the main call that accepts plot arguments, which is not necessarily the top-level call.
automatically evaluating variables that have been stored in a local environment (playState$env).
converting lists to language objects as needed.
enforcing exact matching of argument names exact=TRUE (see [[).

Examples

Run this code

if (interactive()) {

library(lattice)
playwith(xyplot(1:10 ~ 1:10))
playState <- playDevCur()

callArg(playState, "pch")  ## NULL
callArg(playState, "pch") <- "$"
callArg(playState, "pch")  ## "$"
playReplot(playState)

## referring to local variables
tmp <- "x"
callArg(playState, quote(scales[[tmp]]$cex)) <- 2
playReplot(playState)

}