Placeholder Identity Helpers

These are the plain-R callables returned by registering the five built-in ggpaintr placeholders (ppVar, ppNum, ppText, ppExpr, ppUpload). Inside a formula passed to ptr_app() / ptr_server() the parser recognises calls to these names as placeholder invocations and binds them to Shiny widgets (see vignette("ggpaintr-tutorial")). Outside ptr_app() they behave as plain R functions: the first four return their argument unchanged (identity), so a formula such as aes(x = ppVar(mpg)) evaluates identically to aes(x = mpg) under ggplot2's tidy-eval. ppUpload is identical when called with an argument (ppUpload(penguins) returns penguins), so a formula such as ppUpload(penguins) |> filter(...) |> ggplot(...) evaluates as plain R when penguins is in scope. The no-arg form ppUpload() aborts outside ptr_app() — it is meaningful only as a placeholder slot.

Usage

ppVar(x = NULL, ...)

ppNum(x = NULL, ...)

ppText(x = NULL, ...)

ppExpr(x = NULL, ...)

ppUpload(x, ...)

Arguments

x

A column name (ppVar), numeric (ppNum), string (ppText), expression (ppExpr), or dataset name/value (ppUpload). Passed through unchanged.

...

Additional arguments (e.g. named arguments consumed by a custom placeholder's named_args schema). Ignored by the built-in identity implementation.

Value

The input value unchanged. The no-arg form ppUpload() does not return; it aborts with a guard message.

Examples

# Identity inside ggplot2's tidy-eval:
library(ggplot2)
p1 <- ggplot(mtcars, aes(x = mpg)) + geom_histogram(bins = 10)
p2 <- ggplot(mtcars, aes(x = ppVar(mpg))) + geom_histogram(bins = 10)
# p1 and p2 produce the same plot.

# Inside ptr_app() / ptr_server(), the same call binds to a column picker:
if (interactive()) {
  ptr_app(ggplot(mtcars, aes(x = ppVar(mpg), y = ppVar(wt))) + geom_point())
}