callArg: Work with plot call arguments
In floybix/playwith: A GUI for interactive plots using GTK+

Description Usage Arguments Details Value Author(s) See Also Examples

Part of the playwith Application Programming Interface.

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

mainCall(playState)
mainCall(playState) <- value

updateMainCall(playState)

`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.

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 [[).

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

Felix Andrews felix@nfrac.org

playwith.API

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)

}