gradio: Constructor for radio button widget
In jverzani/gWidgets2: Rewrite of gWidgets API for Simplified GUI Construction

A radio button group allows a user to select one from many items. In gWidgets2 the radio button widget shows 2 or more items. The items are coerced to characters, usually by the underlying toolkit. Use the coerce_with property to set a function, such as as.numeric, to coerce the return value during the svalue code. The items are referred to with the [ method, the selected one with svalue.

Generic for method dispatch

The svalue method returns the radio button label or its index if index=TRUE. Labels are coerced to character by many of the toolkits. To be sure to return a numeric value, one can assign to the coerce_with property, e.g., obj$coerce_with <- as.numeric. For all widgets, if a function is specified to coerce_with it will be called on the value returned by svalue.

For a radio button group, for svalue the value can be referred to by index or label.

Check for repeated items before passing on to set_items

gradio(items, selected = 1, horizontal = FALSE, handler = NULL,
  action = NULL, container = NULL, ..., toolkit = guiToolkit())

.gradio(toolkit, items, selected = 1, horizontal = FALSE, handler = NULL,
  action = NULL, container = NULL, ...)

## S3 method for class 'GRadio'
svalue(obj, index = NULL, drop = TRUE, ...)

## S3 replacement method for class 'GRadio'
 svalue(obj,index=NULL,drop=TRUE,...) <- value

## S3 replacement method for class 'GRadio'
 x[i, j, ...] <- value

`items`	items to select from
`selected`	index of initially selected item
`horizontal`	layout direction
`handler`	A handler assigned to the default change signal. Handlers are called when some event triggers a widget to emit a signal. For each widget some default signal is assumed, and handlers may be assigned to that through `addHandlerChanged` or at construction time. Handlers are functions whose first argument, `h` in the documentation, is a list with atleast two components `obj`, referring to the object emitting the signal and `action`, which passes in user-specified data to parameterize the function call. Handlers may also be added via `addHandlerXXX` methods for the widgets, where `XXX` indicates the signal, with a default signal mapped to `addHandlerChanged` (cf. `addHandler` for a listing). These methods pass back a handler ID that can be used with `blockHandler` and `unblockHandler` to suppress temporarily the calling of the handler.
`action`	User supplied data passed to the handler when it is called
`container`	A parent container. When a widget is created it can be incorporated into the widget heirarchy by passing in a parent container at construction time. (For some toolkits this is not optional, e.g. gWidgets2tcltk or gWidgets2WWW2.)
`...`	These values are passed to the `add` method of the parent container. Examples of values are `expand`, `fill`, and `anchor`, although they're not always supported by a given widget. For more details see add. Occasionally the variable arguments feature has been used to sneak in hidden arguments to toolkit implementations. For example, when using a widget as a menubar object one can specify a parent argument to pass in parent information, similar to how the argument is used with gaction and the dialogs.
`toolkit`	Each widget constructor is passed in the toolkit it will use. This is typically done using the default, which will lookup the toolkit through `guiToolkit`.
`obj`	object of method call
`index`	NULL or logical. If `TRUE` and widget supports it an index, instead of a value will be returned.
`drop`	NULL or logical. If widget supports it, drop will work as it does in a data frame or perhaps someother means.
`value`	items to assigns a choices for the buttons
`x`	`GRadio` object
`i`	button index. Leavel as missing to replace items to select from.
`j`	ignored

if(interactive()) {
  w <- gwindow("Selection widgets")
  g <- gvbox(cont=w)

  fl <- gformlayout(cont=g)
  gcheckbox("checkbox", checked=TRUE, cont=fl, label="checkbox")
  gradio(state.name[1:4], selected=2, horizontal=TRUE, cont=fl, label="gradio")
  gcheckboxgroup(state.name[1:4], horizontal=FALSE, cont=fl, label="checkbox group")

  bg <- ggroup(cont=g)
  gbutton("ok", cont=bg, handler=function(h,...) print(sapply(fl$children, svalue)))



}